UC-NRLF
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WIRELESS
TELEGRAPH
BY ELMER E.BUCHE
Practical \Vireless Telegraphy
A COMPLETE TEXT BOOK
for STUDENTS of
RADIO COMMUNICATION
BY '
ELMER E. BUCHER
Instructing Engineer
Marconi Wireless Telegraph Co. of America
Member Institute of Radio Engineers
Fully Illustrated
WIRELESS PRESS, INC
42 BROAD STREET, NEW YORK
Ubrary
COPYRIGHT, 1917
BY
WIRELESS PRESS. INC.
S. L. PARSONS & CO., INC., Printers, 45 Rose St., New York.
AUTHOR'S NOTE
In preparing this volume, the author has endeavored to give the non-technical student and
the practical telegraphist an understanding of the functioning of present day commercial
wireless telegraph apparatus, and he has varied the usual procedure followed in text books
by covering first in a general way the fundamentals of electricity, electromagnetic induction,
the dynamo, the motor, the motor generator, storage batteries, charging panels, etc., a
knowledge of which is quite as essential to the practical wireless worker as the more com-
plicated phenomena of radio-frequency circuits.
It was not possible in the space available to treat the elements of electricity and
magnetism in detail, but an effort was made to cover some of the more important prin-
ciples to prepare the student to understand the functioning of radio telegraph apparatus.
As in the case of the ordinary electrician working in the more common branches of
electrical practice, one of the first essentials in training a wireless telegraphist in the
practical operation of a radio set is to instil in his mind a thorough understanding of
electrical circuits, i. e., the wiring of electrical apparatus, for only as this all important
knowledge is assimilated is the learner qualified to take charge of a commercial wireless
station ; hence, this book is largely devoted to describing the circuits of practical
radio sets together with a simple explanation of the basic principles of the apparatus
associated therewith.
No attempt therefore has been made to treat the subject with rigid scientific accuracy or
completeness. The idea has been rather to show the student what the apparatus consists of
and how it is manipulated. Only general notions of how and why it operates are presented
and neither completeness of treatment nor rigidly scientific as distinguished from popular and
non-technical use of terms have been attempted.
In selecting the apparatus to be described the author has chosen that which is most widely
in commercial use and such other apparatus as is of general interest. In line with this policy,
systems using radio frequency alternative and direct current arc transmitters have been treat-
ed and chapters on undamped oscillation receivers and Marconi transoceanic wireless tele-
graph apparatus have been included.
The attention of prospective wireless operators is directed to the series of questions
in the Appendix (Section F), which bear particularly on the salient points of a practical
operator's course and which were prepared as a guide for the beginner to qualify him to
take the examination for a Government license certificate.
The student who has knowledge of electrical circuits and requires instruction only in
the details of commercial wireless apparatus is advised to read Chapters Four to Twelve
inclusive, but those who only require a working knowledge of the ship apparatus used in the
American Marconi Company's service are directed to Chapters Nine and Twelve.
One of the first questions often asked by a beginner who has had no previous elec-
trical training or experience is "What is the object of the study of the elements of elec-
tricity and magnetism" or "Why is such instruction required previous to taking up the
subject of wireless apparatus proper?"
To this it may be answered that the functioning of wireless telegraph apparatus is based
upon fundamental electrical and magnetic principles and consequently, when the simple
laws of the magnet and electrical currents are. thoroughly understood the ground is at
least two-thirds gone over. The primary object of the elementary work is to prepare the
student step by step to understand the apparatus for the production of radio-frequent
currents — the currents of extremely high frequency by which the electric waves of wire-
less telegraphy are set into motion. The second object is to explain and describe the
apparatus by which the energy of these currents can be radiated in the form of electric
waves and detected at a distant receiving station, and to explain the apparatus by which
such currents are finally made audible in a telephone receiver or some sort of telegraphic
recording apparatus.
The author desires to acknowledge his indebtedness to the Marconi Wireless Telegraph Co.
of America, the Crocker-Wheeler Manufacturing Co. and the Electric Storage Battery Com-
pany for the loan of photographs, cuts, blue prints, wiring diagrams and literature which have
greatly assisted in the preparation of this work. He has also freely consulted the columns of
the Wireless Age and the Proceedings of the Institute of Radio Engineers.
E. E. B.
New Yor4c, June, 1917. '
oooUlo
CONTENTS
PART I.
MAGNETISM.
THE MAGNETIC CIRCUIT.
J>-jO-£
1. Natural Magnet. 2. Flux. 3. Polarity. 4. Magnetic Induction. 5. Permanent and Temporary
Magnets. 6. Laws of Magnetic Poles. 7. Magnetic Circuit 1
PART II.
THE PRODUCTION OF ELECTROMOTIVE FORCE.
ELECTRIC CURRENT AND CIRCUITS.
8. Electrical Current. 9. Classification of Currents. 10. Electromotive Force. 11. Conductors and
Insulators. 12. Production of Electromotive Force. 13. Electricity by Friction (Static Elec-
tricity). 14. Electricity by Chemical Action (Primary or Secondary Batteries). 15. Secondary
Cell. 16. Current Strength and Quantity. 17. Electrical Resistance. 18. Grouping of Electrical
Cells. 19. Ohm's Law and Practical Application. 20. Divided Circuits. 21. Electrical Work.
22. Electrical Horsepower. 23. Definition of Electrical Units. 24. Current Output and Voltage
of Various Current Sources 4
PART III.
ELECTROMAGNETIC INDUCTION.
THE DYNAMO— THE FLOW OF ALTERNATING CURRENT.
25. Electromagnetism. 26. Magnetic Field About Two Parallel Conductors. 27. The Solenoid.
28. Induced Currents. 29. Mutual Induction. 30. Self-induction. 31. Value of Induced
E. M. F. 32. The Dynamo. 33. Determination of Frequency. 34. Strength of Magnetic Field.
35. Diagram of an Alternating Current Dynamo. 36. Direct Current Dynamo. 37. Shunt,
Series and Compound Wound Dynamos. 38. The Electric Motor. 39. The Effect of Counter
Electromotor Force. 40. Motor with Differential Field Winding. 41. Dynamo and Motor
Armatures. 42. Development of Armature Windings. 43. The Alternating Current Transformer.
44. Electrostatic Capacity. 45. Reactance and Impedance. 46. Capacity Reactance. 47. Lag
and Lead of Alternating Current. 48. Effective Value of Alternating E. M. F. and Current.
49. Measuring Instruments or Electric Meters. 50. Induction Coil. 51. Practical Electric
Circuits 16
PART IV.
MOTOR GENERATORS.
HAND AND AUTOMATIC MOTOR STARTERS.
52. The Motor Generator. 53. Field Rheostats. 54. Dynamotor and Rotary Converter. 55. The
Motor Starter. 56. Automatic Motor Starters. 57. Protective Condensers. 58. Care of the
Motor Generator. 59. How to Remove Motor Generator Armature » 51
/
PART V.
STORAGE BATTERIES AND CHARGING CIRCUITS.
60. The Necessity for a Storage Battery in a Radio Installation. 61. General Construction and
Action. 62. The Charging Process. 63. The Fundamental Actions of a Storage Cell. 64. The
Electrolyte. 65. The Hydrometer. 66. How the Capacity of a Storage Cell is Rated. 67. Funda-
mental Facts Concerning the Storage Cell. 68. How to Charge a Storage Cell. 69. How to
Determine the Value of the Charging Resistance. 70. Lamp Bank Resistance. 71. The Use of
the Ammeter and the Underload Circuit Breaker. 72. The Ampere Hour Meter. 73. Over-
charge. 74. How to Charge a Battery When the Voltage Exceeds That of the Charging Gen-
erator. 75. How to Determine the Polarity of the Charging Generator. 76. Determination of the
State of Charge and Discharge of a Battery. 77. Keeping the Level of the Electrolyte. 78. Pro-
tecting the Cells from Acid Spray. 79. General Instructions for the Portable Chloride Type of
Accumulators. 80. General Operating Instructions for the Exide Cell. 81. The Edison Storage
Battery. 82. The Charge and Discharge of the Edison Cell 67
vi PRACTICAL WIRELESS TELEGRAPHY.
PART VI.
THE RADIO TRANSMITTER.
CONDENSERS— OSCILLATION GENERATORS— RADIATION OF ELECTRICAL WAVES-
DAMPING OF OSCILLATIONS.
Page
83. Methods of Generating Radio Frequency Current. 84. The Condenser. 85. Connections for Con-
densers. 86. How to Place a Charge in a Condenser. 87. Analysis of a Spark Discharge.
88. Effect of Resistance on Oscillations. 89. Electrical Resonance. 90. The Open Circuit
Oscillator. 91. The Length of the Electric Wave. 92. The Determination of Wave Length
From the Inductance and Capacity. 93. Logarithmic Decrement of the Oscillations. 94.
Methods of Exciting Oscillations in an Aerial. 95. The Reaction of Coupled Circuits. 96. The
Standard Waves of Commercial Wireless Telegraphy. 97. Fundamental Circuit of a Complete
Radio Transmitter. 98. Simple Explanation of the Circuits. 99. Numerical Values for a
Standard Radio Set 80
PART VII.
APPLIANCES FOR A RADIO TRANSMITTER.
SPARK DISCHARGERS— OSCILLATION TRANSFORMERS— CONDENSERS— TRANSFORMERS.
100. In General. 101. Spark Dischargers for Radio Telegraphy. 102. Adjustment of the Spark Note.
103. Oscillation Transformers. 104. Aerial Tuning Inductance. 105. The Short Wave Condenser.
106. High Potential Condensers. 107. High Frequency "Choking" Coils. 108. High Voltage
Transformers. 109. Reactance Regulators. 110. Aerial Changeover Switch. 111. Transmitting
Keys 101
PART VIII.
AERIALS OR ANTENNAE.
112. Function of the Aerial. 113. Determination of the Wave Length From the Dimensions of
an Aerial. 114. Fundamental Considerations. 115. Various Types of Aerials. 116. Directional
Aerials. 117. Standard Marconi Aerial. 118. The Deck Insulator. 119. Installation of the
Aerial. 120. Earth Connection. 121. Radiation. 122. Antenna Decrement. 123. Transmis-
sion Range • 116
PART IX.
RECEIVING CIRCUITS, DETECTORS AND TUNING APPARATUS.
STANDARD MARCONI RECEIVING SETS.
,24. In General. 125. The Problem. 126. Simple Receiver. 127. The Inductively Coupled Re-
ceiver. 128. Other Methods of Coupling. 129. The Carborundum Detector and Tuning Cir-
cuits. 130. Adjustment of the Inductively Coupled Tuner. 131. The Action of the Car-
borundum Crystal. 132. Adjustment of Crystal Detectors. 133. Detector Holders. 134. Classi-
fication of the Receiving Detectors. 135. Fleming Valve Detector and Tuning Circuits. 136.
Marconi Type 107-A Tuner. 137. Marconi Magnetic Detector and the Multiple Tuner Circuits
(English Marconi Company). 138. The Marconi Type 106 Receiving Tuner. 139. Marconi
Receiving Tuner Type 101 (American Marconi Company). 140. The Marconi Universal Re-
ceiving Set (English Marconi Company). 141. Electrolytic Detector. 142. The Three Element
Valve Detector. 143. A Repeater Vacuum Valve Circuit. 144. The Vacuum Valve Amplifier.
145. Amplification of Radio Frequencies. 146. The Effects of Distributed Capacity. 147. The
"End Turns" of a Receiving Tuner and End Turn Switches. 148. The Variation of a Radio
Frequency Inductance. 149. Buzzer Excitation Systems. 150. Receiving Telephones. 151. Mi-
crophonic Relays or Sound Intensifiers. 152. Brown Amplifying Relay. 153. Atmospheric
Electricity. 154. The Marconi Balanced Crystal Receiver (English Marconi Company). 155.
Type I Aerial Changeover Switch. 156. Marconi Type 112 Receiving Tuner. 156A. General
Advice for the Manipulation of a Receiving Tuner 129
PART X.
AUXILIARY APPARATUS OR EMERGENCY TRANSMITTERS.
!57. Statute Requirements. 158. Tuned Coil Set. 159. The Electric Storage Battery Company's
Accumulators and Charging Panel 179
CONTENTS. vii
PART XI.
PRACTICAL RADIO MEASUREMENTS.
MEASUREMENT OF WAVE LENGTH— DECREMENT - CALIBRATION— TRANSMITTING AND
RECEIVING APPARATUS.
Page
160. The Importance of Electrical Resonance. 161. Indicators of Resonance. 162. Uses of the
Wavemeter. 163. Simple Use of the Wavemeter. 164. General Instructions for Tuning a
Radio Transmitter. 165. Tuning by the Hot Wire Ammeter. 166. Tuning the 2 K. W. 500
Cycle Panel Transmitter. 167. Determination of Coupling. 168. Plotting of Resonance Curves.
169. Measurement of the Logarithmic Decrement of Damping. 170. Calculation of the Decre-
ment of the Wavemeter (or Decremeter). 171. Wavemeter as a Source of High Frequency
Oscillations. _ 172. Calibration of the Secondary and Primary Circuits of a Receiving Tuner.
173. Calibration of the Open and Closed Circuits Simultaneously. 174. Measurement of the
Natural Oscillating Period of a Coil. 175. Measurement of Electrostatic Capacity. 176. Meas-
urement of the Effective Inductance of a Coil at Radio Frequencies. 177. Calculation of In-
ductance from the Constants of the Coil. 178. Measurement of the Effective Inductance and
Capacity of an Aerial. 179. Calibration of a Wavemeter from a Standard. 180. Measurement
of Mutual Inductance at Radio Frequencies. 181. Comparative Measurement of the Strength
of Incoming Signals. 182. "Tight" and "Loose" Coupling. 183. Measurement of High
Voltages. 184. Tuning and Adjustment Record 188
PART XII.
STANDARD MARINE SETS OF THE AMERICAN MARCONI COMPANY.
PANEL TRANSMITTERS— COMPOSITE TRANSMITTERS.
185. Panel Transmitters. 186. Details of Type P-4 Panel. 187. Description of Apparatus. 188.
Complete Adjustment of Type P-4 Set. 189. Type P-5 Panel Transmitter. 190. Description
of Apparatus. 191. Complete Adjustment of the Type P-5. Set. 192. How to Remove the Arma-
ture of the % K. W. Motor Generator. 193. The 1 K. W. Non-Synchronous Discharger
Transmitter. 194. Description of the Set. 195. Installation. 196. Adjustment of the 1 K. W.
Set. 197. Type "E-2" One-half Kilowatt, 120 Cycle Panel Transmitter. 198. Details of the
Circuits and Apparatus. 199. General Instructions for Tuning and Adjusting. 200. Marconi
2 K. W. 240 Cycle Transmitter. 201. Type P-9 Y* K. W. Cargo Transmitting Set. 202.
Aerial Current and Reduction of Pover. 203. General Instructions for the Panel 223
PART XIII.
MARCONI DIRECTION FINDER OR WIRELESS COMPASS AND ITS
APPLICATION.
204. In General. 205. Description of Equipment. 206. The Direction Finder Aerials. 207. The
Circuit Complete. 208. The Tuned Buzzer Tester. 209. How Current is Induced in the Looped
Aerials. 210. Direction of Magnetic Forces Within the Goniometer. 211. General Instructions
for Operation of the Direction Finder. 212. To find the Direction of a Radio Station 255
PART XIV.
TRANSMITTERS OF UNDAMPED OSCILLATIONS.
ARC GENERATORS— RADIO-FREQUENCY ALTERNATORS— PLIOTRON OSCILLATOR.
213. In General. 214. The Arc Generator. 215. Signalling with the Arc Transmitter. 216. The
Alexanderson High Frequency Alternator. 217. Goldschmidt Radioi-'Frequency Alternator.
218. The Joly System for the Protection of Undamped Oscillations. 219. Marconi's System for
the Production of Continuous Waves. 220. The Pliotron Oscillator 264
PART XV.
RECEIVERS FOR UNDAMPED OSCILLATIONS OR CONTINUOUS WAVES.
221. The Problem. 222. The Tikker. 223. The Heterodyne System. 224. The Vacuum Valve as
a Source of Radio-Frequency Oscillations. 225. Vacuum Valve as a Combined Detector,
Amplifier and Beat Receiver. 226. Oscillating Vacuum Valve Detector Circuits of the U. S.
Navy. 227. The Goldschmidt Tone Wheel. 228. Marconi System for Reception of Undamped
Oscillations , 277
PART XVI.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
229. Marconi Development and General Considerations. 230. Marconi's Duplex System. 231. The
Balancing Out Aerial. 232. Glace Bay-Clifden Stations. 233. Marconi Directional Aerial.
234. Marconi Transoceanic Stations. 235. Marconi Tubular Masts. 236. Radio-Frequency
Circuits of the Damped Wave Transmitters. 237. Other U. S. High Power Stations. 238. Long
Distance Receiving Sets. 239. Condensed List of High Power Stations 288
Practical Wireless Telegraphy
PART I.
MAGNETISM.
THE MAGNETIC CIRCUIT.
1. NATURAL MAGNET. 2. FLUX. 3. POLARITY. 4. MAGNETIC
INDUCTION. 5. PERMANENT AND TEMPORARY MAGNETS.
6. LAWS OF MAGNETIC POLES. 7. MAGNETIC CIRCUIT.
Because the flow of an electrical current is invariably accompanied by a mag-
ictic field, a brief explanation of the phenomena surrounding the simple bar
nagnet will be given. This is to be followed in a successive chapter by a descrip-
ion of the electromagnet.
1. Natural Magnet. — A substance which has the property of attracting
>its of iron or steel is called a magnet. Natural magnets found in various parts of
he earth are known as lodestone and a piece of lodestone dipped into a pile of
ron or steel filings exhibits this property of attraction to a considerable degree.
If a bar of hard steel be rubbed with a piece of lodestone the steel is found to
)e magnetized and is then known as an artificial magnet. If the same bar is
lipped into a pile of iron filings, the majority of the filings cling to the tips of the
>ar, there being no tendency towards attraction at the center. Since the strongest
nagnetism exists at the ends of the bar, these ends are known as the poles of the
nagnet.
2. Flux. — If a piece of paper, over which iron filings have been sprinkled,
s placed above and parallel to a bar magnet, the filings will arrange themselves
^ _^ into a series of well defined lines as in
^"" ~^^N Fig. 1. These may be said to show the
/ ,--—•• -^ NN general direction of the magnetic force.
\ I /' ^NN \ / These lines indicate that the space about
\ * / ^ -•*--»„ \ f. *' the poles of a magnet is in a state of
\ \ \ ' / / / ' . stress or strain, and therefore, they are
called the magnetic lines of force or
simply lines of force. The space sub-
' \ \ "\ N jected to this strain is called the mag-
^__^ -' i \ \ netic field and the total lines of force
1 \ crossing a given space or field are
/
^-~^ — - / termed the magnetic flux.
3. Polarity. — A magnetic needle
Fig. i-Fieidf a Simple Bar Magnet. suspended or pivoted as in a compass
and left to swing freely will, as is well
known, point in the direction of the north magnetic pole. The end which points
in that direction is known as the north pole of the magnet and the opposite end,
the south pole.
2 PRACTICAL ; WIRELESS TELEGRAPHY
4. Magnetic Induction.— A' piqce of soft iron placed in the magnetic field
of another niftgixct, ". fcrecoja'Jes .temporarily magnetized and will have two unlike
poles. Magnetism H'htis ; indtice(i in a piece of soft iron is said to be due to
magnetic induction. If, for example, the north pole of a steel bar magnet be
placed near to a bar of soft iron, the end of the iron bar nearest to the magnet
will exhibit south magnetism and the opposite end north magnetism. It should
be understood that magnetism can be induced in the iron bar whether in direct
contact with the inducing magnet or slightly separated from it but when the
exciting magnet is removed, the induced magnetism will practically disappear.
5. Permanent and Temporary Magnets. — Because a bar of soft iron re-
tains its magnetism only while under the influence of a given magnetizing force
it is called a temporary magnet. On the other hand a piece of steel, when once
magnetized, retains its magnetism permanently, and thereafter is known as a
permanent magnet.
LINES IN OPPOSITE DIRECTION
REPULSION
LINES IN SAME D1RECT10H
ATTRACTION
m
.-•>)} rcc
Fig. 2 — Diagram Showing the Attraction and Repulsion of Magnetic Fields.
The power of steel to resist magnetization and once in this condition to resist
demagnetization is termed its retentivity. Steel possesses greater reten-
tivity than iron because, as previously mentioned, soft iron becomes saturated
with magnetism very quickly and loses it almost immediately when the inducing
magnetic field is removed.
The capability of any substance for conducting magnetic lines of force is
termed its permeability. Iron, for instance, possesses much greater permeability
MAGNETISM. 3
•
than steel and steel possesses greater permeability than air. This means
that if the circuit for the magnetic lines of force from pole to pole of a magnet
is completed through an iron core, a greater number of lines of force will pass
than if the circuit were completed through a piece of steel or through air.
6. Laws of Magnetic Poles. — If two bar magnets are suspended by a cord
as in Fig. 2, and the north pole of one brought near to the north pole of the
other, they will be found to repel. On the other hand, if the south pole of a bar
magnet is brought near to the north pole of another magnet, they are found to
attract one another. The foregoing actions may be summed up by the funda-
mental law : Like magnetic poles repel, unlike magnetic poles attract.
A variation of this law is encountered when a very strong south pole, let us
say, is placed near a weak south pole. The stronger magnet will attract the weaker
one because of its over-powering field. Similar effects are observed between two
north poles of dissimilar strength.
7. Magnetic Circuit. — Each line of force of a magnet (as in Fig. 1) is
assumed to pass from the south pole to the north pole, through the bar and
from the north to the south pole outside the bar. This is said to be the direction
of the lines of force and the path they take is called the magnetic circuit. Such a
circuit is usually made up of magnetic material like iron or steel but in com-
mercial apparatus very often one or more air gaps are included in the path of the
flux.
If a magnetic substance such as a bar of iron is suspended free to move in a magnetic field,
it ivill tend to turn and lie parallel with the Held, or, as is more often said, ^vill take such a
position as to accommodate through itself the greatest number of lines of force. On the other
hand, if a permanent magnet is suspended free to move in a magnetic field of definite direction
(such as suspending a bar magnet above a stationary magnet} it will tend to take a parallel
position with the field but in a particular direction, that is, its internal lines of force will be
in the same direction as those of the field.
Advantage of this fundamental principle is taken in the design of many electromagnetic
devices and in electrical measuring instruments to be described later on.
Powerful magnetic fields may be created by an electric current. Mag-
netism so produced is known as electromagnetism. The great advantage of the
electromagnet is the fact that the strength of the magnetic field can always be
controlled, whereas the field of the permanent magnet is more or less of fixed
strength. Electromagnetism will be taken up in its proper order in a following
chapter.
PART II.
THE PRODUCTION OF ELECTROMOTIVE
FORCE.
ELECTRIC CURRENT AND CIRCUITS.
8. ELECTRICAL CURRENT. 9. CLASSIFICATION OF CURRENTS.
10. ELECTROMOTIVE FORCE. 11. CONDUCTORS AND INSULA-
TORS. 12. PRODUCTION OF ELECTROMOTIVE FORCE. 13. ELEC-
TRICITY BY FRICTION (STATIC ELECTRICITY). 14. ELECTRICITY
BY CHEMICAL ACTION (PRIMARY OR SECONDARY BATTERIES).
15. SECONDARY CELL. 16. CURRENT STRENGTH AND QUANTITY.
17. ELECTRICAL RESISTANCE. 18. GROUPING OF ELECTRICAL
CELLS. 19. OHM'S LAW AND PRACTICAL APPLICATION.
20. DIVIDED CIRCUITS. 21. ELECTRICAL WORK. 22. ELECTRICAL
HORSEPOWER. 23. DEFINITION OF ELECTRICAL UNITS. 24. CUR-
RENT OUTPUT AND VOLTAGE OF VARIOUS CURRENT SOURCES.
8. Electric Current. — When we speak of a current of electricity as flowing
through a wire or circuit we simply express in a convenient way certain
phenomena associated therewith. We do not, in fact, know what actually trans-
pires in the transfer of electricity from point to point in a conductor. Electricians
generally agree that a so-called "current" of electricity flows in a definite direc-
tion throughout a given circuit, but there is no direct evidence at hand to prove
the actual existence of a "current", in the commonly accepted meaning of the
word. The term, however, is universally adopted to designate the flow of elec-
tricity from point to point in an electrical circuit.
9. Classification of Currents. — Electrical currents are called direct if they
flow in one direction throughout a given circuit, and alternating if they con-
tinually reverse, flowing first in one direction and then in the other.
A primary current is said to be one which flows directly from a generating
source. A secondary current is one induced by a primary current acting in-
ductively on a circuit having no direct connection with the primary circuit.
A current is said to be of low tension when its pressure or voltage is rela-
tively low, and conversely, it is said to be of high tension when its pressure
or voltage is relatively high.
10. Electromotive Force. — In order to produce a steady electrical current,
two conditions are necessary. There must be a steadily maintained electric
pressure known as electromotive force and a suitable conducting path to pass
the current.
11. Conductors and Insulators. — A metallic circuit in which a current of
electricity flows with little opposition is said to be a conductor; one which
offers considerable resistance is known as a partial conductor, but a substance
which completely impedes the flow of current is termed an insulator. It should
be understood at the beginning that these terms are purely relative for an abso-
lute insulator or a perfect conductor does not exist.
The best conductors of an electric current among the common metals, in order of
their increasing resistance, are silver, copper, gold, aluminum, zinc, iron, platinum and
nickel.
Examples of insulators given in order of their increasing value are dry air, shellac,
THE PRODUCTION OF ELECTROMOTIVE FORCE.
paraffine, amber, resin, sulphur, wax, glass, mica, ebonite, india rubber, silk, paper
and oils.
12. Production of Electromotive Force. — To produce an electromotive
force, it is necessary first to create a difference in potential or difference in electric
pressure between two bodies or two points in the same body.
An electromotive force can be produced by various methods, for example :
(1) By friction (static machine);
(2) By chemical action (primary and secondary batteries) ;
(3) By mechanical motion (dynamos or generators) ;
(4) By thermal action (thermo junction).
In the following chapters these four methods will be considered consecutively
and in detail.
Electromotive force is denoted by the unit termed the volt. The term
pressure and voltage are used to express difference of potential or electromotive
force (abbreviated E. M. E.) as well.
13. Electricity by Friction (Static Electricity).— When a piece of amber
is rubbed with silk the amber is said to be electrified, and the presence of this
electrification can be detected by holding the amber near to small bits of paper.
The paper will be attracted to the amber. The silk is also in a state of electri-
fication and if it is held near to another piece, similarly electrified, it will be
repelled. Likewise two pieces of electrified amber will repel one another, and
if the amber is held near the silk, the silk will be attracted to it.
This action of attraction and repulsion is said to be due to electric charges
residing on these elements. The amber is said to possess positive ( + ) electri-
fication and the silk negative ( — ) electrification. The electric charges are
said to be caused by friction and are known as static electricity, meaning electric
charges at rest or stationary.
It is to be noted that if a body containing a positive charge is brought
in contact with one containing a negative charge, both charges being of equal
intensity, they will neutralize and disappear ; the bodies are then to be discharged.
Again if two charged bodies are joined by an electric conductor, all signs of
electrification will disappear and there will pass through the conductor a momen-
tary electric current.
There are other elements which when
rubbed together will produce static charges
of electricity, but the foregoing example
is sufficient to illustrate the method.
Machines for the production of electro-
motive force by friction are known as
static or frictional machines but since they
bear no particular relation to the principles
involved in the functioning of wireless tele-
graph apparatus, a description will not be
given.
14. Electricity by Chemical Action
(Primary or Secondary Batteries). —
A convenient and practical appar-
atus for setting up a steady electro-
motive force is the electrochemical
cell which consists of two dissimilar
elements, in other words, two un-
like metals immersed into a dilute
acid or alkali solution.
A simple cell, for example, consists of
strips of zinc and carbon immersed in a
conducting solution of sal ammoniac (am-
monium chloride) as in Fig. 3. If the Fig. 3— Simple Electric Cell.
6 PRACTICAL WIRELESS TELEGRAPHY
exposed terminals of these plates are joined by a metallic conductor, the cell is capable of
supplying a continuous flow of electricity through the wire. It is observed as the current
flows that the zinc strip wastes away, in fact, the consumption of the zinc furnishes the electro-
motive force necessary to drive the current through the cell and through the external circuit.
The chemical changes within the cell, consisting of copper and zinc strips immersed in a
dilute solution of sulphuric acid may be briefly described as follows: When the copper
and zinc strips are connected together by a metallic circuit and the current begins to
flow, the sulphuric acid attacks the surface of the zinc plate and forms a compound known
as sulphate of zinc. During the formation of this sulphate some of the hydrogen contained
in the sulphuric acid is liberated in the form of bubbles which immediately appear on the
copper plate. Some of these bubbles rise to the surface of the liquid and escape into sur-
rounding air, but others cling to the copper plate which gradually becomes covered with a
film of hydrogen. Since hydrogen is a non-conductor of electricity, the amount of surface
of the copper plate in contact with the battery solution gradually decreases as the accumula-
tion of hydrogen gas increases, and accordingly the current output of the cell diminishes.
In electrician's parlance the cell is now said to be "run down." Part of. this reduction of
current is due to the fact that hydrogen tends to set up a current within the. cell in the
opposite direction to the normal flow as well as cover the copper plate. A cell in this
condition is said to be polarized, and various chemical and mechanical means have been
devised to prevent the hydrogen bubbles clinging to the copper plate.
An electroscope (a device for determining the presence and nature of electric
charges) indicates a strongly negative charge at the exposed end of the zinc
element. The zinc plate is therefore known as the negative ( — ) pole of the
cell, and the carbon or copper terminal, the positive ( + ) pole of the cell.
We learn from this that the action of the battery solution upon one plate more
than on the other tends to keep the plates in a continuous state of electrification,
the stronger manifestation being exhibited at the exposed end of the zinc plate
and it is this difference in pressure which causes the current to flow round the
external circuit.
The direction of the current inside the cell will be from the zinc plate through
the solution to the carbon plate and outside the cell from the carbon plate through
a metallic conductor to the zinc plate.
The conducting fluid in which the elements of the electric cell are immersed
is known as the electrolyte or the exciting fluid. The plates and the metallic
terminals attached thereto are termed the poles or electrodes of the cell. A
number of cells connected together are known as a battery.
The type of cell just described is called a primary cell to distinguish it from
a storage or secondary cell which will be described in detail further on.
It has been mentioned that the electromotive force or corresponding flow of current pro-
duced by the electrochemical cell is caused by two dissimilar elements. The list of metals
given below are arranged in such order that any single element will be the negative pole of
the battery when used with the metal next below it on the list, and the positive pole when
used with the element next above it.
( — ) Sodium Iron *
Magnesium Copper
Zinc Silver
Tin Gold
Cadmium Platinum
Lead Carbon (+)
Referring to this list, although there will be a difference of potential, and consequently a flow
of current between carbon and copper if joined together by a wire and immersed in a battery
solution, there will be a very much greater electromotive force if carbon and zinc are employed.
15. Secondary Cell. — A simple secondary cell popularly known as a
"storage battery" consists of two or more plates of lead placed in a dilute
solution of sulphuric acid as in Fig. 4. One of the plates in this diagram is
connected to the positive terminal of two primary cells (connected in series)
and the other plate to the negative terminal. When current flows from
the primary battery for some time through the solution from plate to plate as in
Fig. 5 and afterwards the wires from the primary battery are disconnected and
FOOTNOTE:— Cells of various types are described in books on elementary electricity to which the reader is
referred for a more detailed description.
THE PRODUCTION OF ELECTROMOTIVE FORCE.
ANODE
LEAD mp^ m
SECONDARY
CELLS
..CATHODE
the plates are joined by a conductor, current will flow from the lead plate which
was connected to the positive terminal of the primary battery to the opposite lead
plate, and within the cell, in the opposite direction.
j , f ; When the current flows from plate to
plate through the electrolyte, the plate
connected to the positive pole of the battery
receives a brown coating of peroxide of
lead but the opposite plate becomes spongy
or porous. Since the passage of the cur-
rent through the cell has left one plate
unchanged while it has coated the surface
of the other plate with lead peroxide, it is
reasonable to expect that if the charging
battery is disconnected and the two dis-
similar lead plates connected by a wire, a
current of electricity will flow through the
external circuit. In fact, we now have the
essentials of an ordinary chemical cell.
This cell will continue to supply current
until the lead peroxide is partly used up
and the plates will gradually return to the
state they were in before the charging
process took place. In order that the
plates may be put in condition to deliver
PRIMARY
CELLS
Fig. 4 — Simple Diagram for
Cell.
"Charging" a Storage
current again, they must be reconnected to the charging source and a new coating of
peroxide of lead deposited upon the positive plate. It will be seen, therefore, that it is not
really electricity which is "stored up" in the storage cell but that the current supplied to the
cell during the charging process produces an electrochemical change which gives the plates
dissimilar properties, and so long as this change is evident, there will be a difference of
potential at the terminals and therefore an electromotive force. In commercial practice
storage cells are "charged" by electric dynamos or generators rather than by primary cells.
The electromotive force of primary cells varies from .06 to 1.5 volts according
to the nature of the battery elements
and the grade of electrolyte. The
electromotive force of the lead plate
secondary cell lies between 2.1 and
2.6 volts.
In electrical equations, potential
or E. M. F. is represented by the
letter E. Instruments for measur-
ing potential difference are known
as "voltmeters.
16. Current Strength and Quan-
tity.— Up to this point we have not
made mention of the strength of
the current or the quantity of elec-
tricity flowing through a given cir-
cuit. We have simply referred to the
potential difference and the conse-
quent electromotive force generated
by chemical cells. Just as we might
use in the system of hydraulics the
gallon per second as a unit to express
the quantity of water flowing from
a given source, so in electrical cir-
cuits, we express the quantity of
electricity flowing by the Unit Fig. S-Elemental Storage Cell.
8 PRACTICAL WIRELESS TELEGRAPHY
termed the coulomb. We must not confound the measure of the total quantity
of electricity in a given circuit with its strength or rate of flow. The strength of
an electrical current should be described as the rate of flow of electricity through
a circuit per second of time. When one practical unit of quantity of electricity
(one coulomb) flows every second continuously, the rate of flow or the strength
of the current is said to be one ampere; if three unit quantities flow continuously
every second, the strength of the current is three amperes and so on. Hence iJc
may define the ampere as the quantity of electricity flowing past any point in a
circuit per second of time.
The strength of the current in amperes will be seen to be independent of the
length of time the current flows in a given circuit whether it flows for a fraction of
a second, a minute, or an hour ; if the quantity of electricity that would flow in one
second is the same in any two or more cases the current in amperes is the same.
We may now define the coulomb as the amount of electricity that would pass
in one second through a given circuit in which the strength of the current is one
ampere.
If a current of one ampere flows every three seconds, the quantity of electricity
delivered is three coulombs, or if three amperes of current flow for one second,
the quantity is also three coulombs. From this we see that the quantity of
electricity in coulombs is equal to the current strength in amperes multiplied by
the time it flows in seconds or,
0= I X t,
Where Q = Quantity of current "in coulombs,
I = Current in amperes,
and t = Time in seconds.
Hence to find out the quantity of electricity that flows around a circuit in ten minutes
when the strength of the current is ten amperes, we substitute the value of I and t in this
equation and multiply or, Q = 10 X 600 — 6,000 coulombs.
It is more convenient in electrical practice to measure the strength of the current in
amperes than to compute the total quantity of electricity flowing ; hence, when we speak of
the current available from a given electrical source, we employ the unit, the ampere, which
indicates the rate at which it flows.
In electrical equations the ampere is represented by the letter I. Instruments
for measuring the strength of current are called ampere-meters or ammeters.
17. Electrical Resistance. — If the terminals of a primary or secondary
cell, or a battery of cells, are connected to a length of copper wire and a current
measuring instrument such as the ammeter, connected in series with the circuit,
a much greater reading or deflection of the ammeter will be obtained with a
given length of copper wire than with an iron wire of the same length and
diameter. This experiment indicates that a cell producing a constant E. M. F.
(abbreviation for electromotive force) can force a very much stronger current
through a copper wire than through an iron wire of the same proportions. We
may conclude from this that iron offers a higher resistance to the passage of
electricity than copper.
Resistance in electrical circuits may be defined as that property of bodies which
opposes the flow of electric current. Just as water passes with difficulty through
a small pipe of great length, but very freely through a large pipe of short length
so, also, a small wire of considerable length and poor conducting qualities opposes
the flow of electricity considerably, but a good conductor of short length and
large diameter offers but very little resistance.
All substances are found to resist the passage of electricity but the resistance
of metals is by far the least. Of all metals, silver is found to be the best con-
ductor, and it therefore possesses less resistance than copper, for example. In
fact, the ability of silver to conduct electricity is taken as unity or the base from
which the specific resistance of other metals is computed.
The specific resistance of any material is the resistance of a piece of unit length and unit
THE PRODUCTION OF ELECTROMOTIVE FORCE. 9
cross section at an arbitrarily adopted degree of temperature. It is, in fact, the resistance
of an inch cube of any substance at the temperature of melting ice.
The following table shows the relative resistance of chemically pure metals at the tem-
perature of 32 degrees Fahrenheit. Resistance in Microhms
Metal Relative Resistance per cubic inch
Silver annealed 1.000 .5904
Copper annealed 1.063 .6274
Silver hard drawn 1.086 .6415
Copper hard drawn 1.086 .6415
Gold annealed 1.369 .8079
Aluminum annealed 1.935 1.144
Zinc pressed 3.741 2.209
Platinum 6.022 3.555
Iron annealed 6.460 3.814
Lead 13.05 7.706
German Silver 13.92 8.217
We learn from this table that a cubic inch of German silver, for instance, has a little
more than 13 times the specific resistance of a cubic inch of annealed silver.
We find by experiment that the total resistance of a conductor varies directly as the
specific resistance and length, and inversely as the cross sectional area. These quantities
are related in the following way :
L
R_ c
— «J >
A
where R = the resistance in ohms ;
L = the length of the conductor ;
A = its cross sectional area;
S = the specific resistance of the material.
Hence if we know the length and cross sectional area of a conductor, take the value of
S from the foregoing table and substitute all three values in this formula, the total re-
sistance is readily determined.
The resistance of metals is also affected by temperature; usually it increases with in-
crease of temperature but certain substances decrease their resistance under rise of tem-
perature, an example being carbon lamp filaments and certain electrolytic conductors such
as battery solutions. The hot resistance of the carbon filament of an incandescent lamp
is approximately one-half the value when cold. The resistance of a conductor, however,
is always constant, if the temperature remains constant, irrespective of the strength of
current flowing through it. If a conductor offers unit resistance to a current of one
ampere, it offers the same resistance to a current of twenty amperes provided the tempera-
ture does not change appreciably. In most circuits encountered in practice, the rise of
temperature is not appreciable, but in case a conductor does heat considerably, the actual
resistance can only be obtained by taking the temperature into account as well as the
specific resistance.
The unit of resistance is called the ohm. The international ohm is the re-
sistance offered to the flow of an unvarying electric current by a column of
mercury 106.3 centimeters long, weighing 14.4521 grams, at a temperature of 32
degrees Fahrenheit.
Examples of conductors in ordinary electrical practice having approximately this value
of resistance follow :
1 ohm = 250 ft. of No. 16 B. and S. copper wire, which is l-20th of an inch in diameter.
1 ohm =r 1,000 ft. of No. 10 B. and S. copper wire, which is l-10th of an inch in diameter.
One thousand feet of No. 32 B. and S. bare copper wire has resistance of 170.7 ohms.
In electrical equations resistance is expressed by the letter R.
18. Grouping of Electrical Cells. — Battery cells may he grouped in three
ways :
(1) In series;
(2) In parallel;
(3) In series multiple or series parallel.
Keeping in mind the units for expressing the strength and pressure of an
electric current, we shall now see how the grouping of cells in various ways affects
the current and pressure available for a given external circuit.
10
PRACTICAL WIRELESS TELEGRAPHY
rL5Vi
A series connection is made by joining the positive pole (the carbon plate) of
one cell to the negative pole (zinc plate) of the next cell, as shown in the diagram,
Fig. 6. The upper part of this dia-
gram shows two chemical cells con-
nected in series and the lower figure
shows ten cells connected in series
as they would be represented in or-
dinary electrical diagrams.
In the upper diagram of Fig. 6, current
flows from the carbon plate of the cell
through the switch S, through a concen-
trated resistance coil R (which may be of
German silver or other metal of high
specific resistance) to the zinc plate of the
right hand cell. The circuit continues
from the zinc plate through the electrolyte
to the carbon plate, from the carbon plate
to the zinc plate of the left hand cell, and
finally through the electrolyte to the carbon
plate from which the flow originally began.
When the switch S in this diagram is
opened, the circuit from the battery cells
is said to be broken or interrupted; but
S
U-
1.5V
vvvvvvv
R
1 r
c
t ii
§&
I
1
c
1
1
1
1
1
i«;
I
i
I
I
I
i!
*
r^
Fig. 6 — Electric Cells Joined in Series.
when switch S is closed, the circuit it called
a closed circuit, current flowing freely from the positive to the negative pole of the battery.
Now the total resistance of this circuit is made up of the resistance coil R, the re-
sistance of the connecting leads and the internal resistance of the battery cells, that is the
resistance of the electrolyte from plate to plate. The strength of the current flowing
through this circuit, as will be explained in detail further on, is governed by the total
E. M. F. of the cells and the total resistance of the circuit and since the internal resistance
of ordinary primary cells is rather high, it cannot be ignored in the grouping of cells.
When cells are connected in series, the total electromotive force is that of one cell
multiplied by the number of cells in the group (provided all cells have identical potential) ;
but the strength of the current will not exceed that of a single cell, and more likely will
be less, due to the fact that the total resistance of the circuit increases as more cells are
added (o the battery. Grouping of the cells in either series or parallel affects the total
internal resistance as follows : When a number of cells in a battery are connected in series,
the total internal resistance is equal to the sum of the internal resistances of all the cells.
When a number of like cells are connected
in parallel, the total internal resistance is
equal to the resistance of one cell divided 1-5 V
by the number of cells in the battery.
A parallel connection is made by
connecting the positive terminal of one
cell with the positive terminal of an-
other cell and the negative terminal
of the first cell with the negative
terminal of the second cell as in the
diagram Fig. 7. The left hand figure
shows the direction of the flow of cur-
rent of two cells connected in parallel
and by this connection, the total
electromotive force of the cells is no
more than that of a single cell but the
current available (in amperes) is that
of one cell multiplied by the number
of cells in the group.
Applying this to the right hand dia-
gram of Fig. 7 where four cells are con-
v VWWWV — — J
+
• —
1.
5V
1
5V
fc
5V
+
I~
R
v VWWWV—
9 OHMS
Fig. 7 — Electric Cells Joined in Parallel.
THE PRODUCTION OF ELECTROMOTIVE FORCE.
11
UNIT A 3- 1.5V -4.5V
nected in parallel, the potential difference across the terminals is 1.5 volts and the current
available in amperes will be 4 X 15 or 60 amperes. If the resistance of R is rather high,
of the order of a few hundred ohms, this potential difference can be measured by connect-
ing a voltmeter across the terminals. It should indicate E. M. F. of \y2 volts. We see
from this that the final effect of a parallel connection in the case cited is the same as if 4
zinc plates joined together and 4 carbon
plates joined together were immersed in a
single battery tank.
A series parallel connection of
electrical cells is shown in the dia-
gram, Fig-. 8, where groups A and B
each * consist of three battery cells
joined in series and shunted by the
resistance R.
Since groups A and B consist of three
cells connected in series, then (in accord-
ance with the statements made concerning
III
UNIT "B 3»I.5V«4.5V
III
R = 45 OHVAS
-vvwww
4.5 VOLTS
Fig. S; — Cells Grouped in Series Parallel.
series connection of cells in previous para-
graphs) the voltage of each group will be
3 X 1.5 or 4.5 volts, but the current avail-
able from either groups A or B will not
be greater than that of a single cell in
either unit. Assuming that each group is
capable of delivering current of 15 amperes, there will be available for the external circuit
15 -f- 15 or 30 amperes, but the total electromotive force of the two groups is that only of
one group or 4.5 volts.
When the resistance of the external circuit is small in comparison with the
internal resistance of the cells, there is no advantage in the series connection be-
cause the flow of current will be governed by the resistance of the battery rather
than by the external circuit. In this case parallel grouping of the cells is most
desirable. When the external resistance is large in comparison with the internal
resistance of a single cell, the cells are most advantageously connected in series.
It is thus plain that the connection to be adopted will depend upon the resistance
of the external circuit as compared to that of the internal resistance of the battery.
In the majority of cases, the most efficient grouping is the one where the internal
resistance of the cells about equals the resistance of the external circuit.
19. Ohm's Law and Practical Application. — The relation between electro-
motive force, current strength and the resistance of an electrical circuit is dis-
closed by Ohm's law which states that the strength of the current in amperes in
any given circuit is directly proportional to the E. M. F. and inversely proportional
to the resistance, or using the symbols of the previous paragraph,
E
I = -
R
which may be written
Volts
Amperes =
Ohms
The student cannot overestimate the importance of this law because only as it
is thoroughly understood can electrical circuits be handled and cared for intelli-
gently. Applying the law practically, if an E. M. F. of 6 volts is applied to a circuit
having a total resistance of 3 ohms, the current strength in amperes is obtained as
follows :
6
I = - =z 2 amperes
3
By transposing this equation we may write
12 PRACTICAL WIRELESS TELEGRAPHY
E = I X R
E
or R = —
I
It is plainly evident that if we know any two of the quantities involved in this
expression, the third may be readily determined.
To illustrate : If the flow of current in a given circuit is 2 amperes and its total re-
sistance 220 ohms, the E. M. F. applied to set up this value of current must have been.
220 X 2 = 440 volts (E = I X R).
As a second illustration we may take the case of an ordinary carbon filament carbon
lamp which takes 0.5 amperes under pressure of 110 volts. According to this law, the
110 E
resistance of the filament must be or 220 ohms (R = — ).
0.5 I
We learn from Ohm's equation that to increase the flow of current through a
circuit of fixed resistance we must increase the voltage. If the voltage be doubled,
the flow of current is doubled and so on. By the same law if the flow of current
through a given device and the pressure across its terminals can be measured, the
resistance in ohms is obtained by simply dividing the pressure in volts by the
current in amperes. •
Ohm's law applied to the circuit of Fig. 6 yields the following results : If the coil R
has a resistance of 9 ohms and the E. M. F. of the cells is 3 volts, the strength of the cur-
3
rent through R = — = 0.33 amperes (assuming the internal resistance of the cells and
9
connecting wires to be negligible). If R had 18 ohms resistance, 0.166 amperes would flow
through the circuit. If, in the left hand drawing, Fig. 7, R has 9 ohms resistance and the
1.5
E. M. F. is V/2 volts, the current = — = 0.16 amperes. Also if R in Fig. 8 had resistance
9
4.5
of 9 ohms, the flow of current would be — or 0.5 amperes.
9
If a number of electrical devices are connected in series as in diagram, Fig. 9, the cur-
rent through each element is the same, irrespective of its resistance. In this diagram a
source sf direct current potential B, of 100 volts is applied to the circuit comprising an
electric lamp L, of 180 ohms, a resistance coil R, of 50 ohms, and a telegraph sounder S, of
4 ohms. We may calculate the current flowing at any point through the circuit such as at
A, by first determining the total resistance. This, exclusive of the cells and connecting
100
wires leading therefrom, is 180 + 50 + 10 = 240 ohms; the current in amperes — -
240
0.41 amperes.
It is to be especially noted that the strength of the current through all the elements of
this circuit is the same, irrespective of the resistance of the individual elements but the
current is governed principally by the greater resistance, that of the lamp L.
If a voltmeter be connected to the terminals of any of the various resistance
elements of the circuit (see V in Fig.
^-;fv 9),. a difference of potential or elec-
(TD r~VV~~~! tromotive force will be found to exist
across the terminals that varies as the
resistance and the strength of the cur-
rent. The electromotive force may
Ttenpl be calculated directly by Ohm's law
si -^- anil if the resistance and the current are
R
50 OHMi
I — j~— known jf the current flowing
L 10 OHMS , , . .
^^ through each resistance element is
— -""^^ 0.41 amperes, the pressure in volts is
Fig. 9— Electrical Devices Connected in Series. obtained by multiplying the current
THE PRODUCTION OF ELECTROMOTIVE FORCE.
13
strength in amperes by the resistance in ohms. Thus the potential difference across
R = 0.41 X 50 = 20.5 volts; similarly across L =- 180 X 0.41 - 73.8 volts (the
calculation being made oruthe assumption that the internal resistance of the
cells is zero).
20. Divided Circuits. — A divided or shunt circuit is an additional circuit
provided at any part of a circuit through which the flow of current sub-divides.
One branch of such a circuit is said to be in multiple or in parallel with the other
branch or branches.
Fig. 10 represents a divided circuit of 3 branches, R-l, R-2 and R-3. If resistances
R-l, R-2 and R-3 are equal, the current flowing from A to B will divide equally between
the 3 branches. If a current of 9 amperes
+ is flowing in the main circuit as indicated
" by the ammeter A, 3 amperes will flow
through each branch. If the resistances
are unequal, the current divides inversely
as their relative resistance.
The current in the branches of the
divided circuit, Fig. 10, can be determined
by finding the voltage across the terminals
of each branch, and dividing the result by
the resistance of each branch.
Thus the current in branch R-l =
E E E
Fig. 10 — Diagram Showing Branch Electrical Circuits. — — ? R-2 — and in R-3 '=. - — .
R-l R-2 R-3
100 100 100
R-l passes - - or 3.33 amperes; R-2 passes - - or 5 amperes and R-3, - - or 10
30 20 10
amperes. An ammeter connected in series with the circuit as at point C should indicate
3.33 -f 5 -f- 10 or 18.33 amperes. (Resistance of the connecting leads being ignored).
When several resistances are connected in parallel their joint resistance is computed as
follows :
R-l
30 OHMS
R-2
20 OHMS
R-3
'0 OHMS
R =
1
where R = the joint resistance.
the 3 elements is equal to:
R-l R-2 R-3
Hence, in the circuit of Fig. 10, the joint resistance of
1
= — =r 5.4 ohms.
11
30 20 10 60
It is now clear that two or -more resistances in parallel will conduct an electric
current more freely than one, and the joint resistance of several resistances in
parallel is less than the resistance of the smaller one.
When a nnmber of resistances are connected in series their joint resistance is
the sum of several resistances taken separately.
21. Electrical Work. — When a current of electricity flows through a con-
ductor, it encounters frictional resistance and a certain amount of the energy is
transformed into heat. The heat of a conductor under certain conditions may be
so great that unless due precaution is taken, the wire will melt. We find that
when an electric current has passed through a substance, the development of heat
is proportional,
(1) To the time during which the current flows;
(2) To the square of the current;
(3) To the resistance of the conductor.
14 PRACTICAL WIRELESS TELEGRAPHY
This may be expressed :
J == I2 X R X T,
where J — the electrical energy expended in the form of heat in joules.
The joule is defined as that amount of energy which is expended during one
second, by current of one ampere flowing through a resistance of 1 ohm and the
joule per second is the practical unit of electrical power which has been named
the ivatt.
joules
Since power is the rate of doing work per unit of time, watts = - — .
time
Hence if 2,000 joules of electrical work are done in twenty seconds, the power exerted
2000
is - - = 100 joules per second — 100 watts. Power may also be expressed in the units
20
of pressure and current strength. The power in watts in a given circuit in which direct
current is flowing is equal to the product obtained by multiplying the current in amperes
hy the electromotive force in volts or
W = I X E.
Hence, if in any given direct current circuit we measure the pressure by a
voltmeter, and the current strength by an ammeter, the power in watts is obtained
by multiplying together the readings of each instrument.
22. Electrical Horsepower. — The unit of mechanical work is a foot
pound. It is the work done in raising a mass of 1 Ib. against the force of gravity
through a distance of 1 ft. Work done at a rate equal to 33,000 ft. Ibs. per minute
is called the horsepower (abbreviated H. P.).
One Mechanical H. P. = 33,000 ft. Ibs. per minute = 550 ft. Ibs. per second. Also it
can be shown that 1 joule = 0.7373 ft. Ibs., hence, 1 joule per second or 1 watt = 0.7373
1 watt
Ibs. per second. Therefore 1 ft. Ib. per second = - — .
0.7373
1 H. P. 1 watt 550
Since 1 ft. Ib. per second = — — or — — , therefore 1 mechanical H. P. =
550 0.7373 0.7373
746 watts.
Now 746 watts = 1 mechanical H. P., therefore
W
H. P. = or,
746
IXE
H. P. =
746
Where I = the current in amperes, E — pressure in volts.
For example, an electric motor requires 30 amperes current at pressure of 110 volts; its
110X30 3300
rating in H. P. = - - = 4.4 horsepower.
746 746
1 kilowatt = 1000 watts = 1.34 H. P.
1 H. P. = 746 watts = .746 K. W.
23. Definition of Electrical Units. — The practical units of electricity may
be defined as follows:
The practical unit of electromotive force is the volt, and by definition the volt
is that E. M. F. required to maintain the flow of current of one ampere through a
resistance of one ohm.
The practical unit of current strength is the ampere, and it is that strength of
current maintained by an E. M. F. of one volt through a resistance of one ohm.
The ohm is the unit of resistance and is such resistance of conductor or circuit
that permits the passage of a current of one ampere under an E. M. F. of one volt.
THE PRODUCTION OF ELECTROMOTIVE FORCE.
15
The unit of current quantity is the coulomb which is the quantity of electricity
flowing in a circuit when one ampere passes a given point during one second of
time.
The watt is the unit of electrical power and is equal to one joule per second.
It is the power of a current of one ampere flowing under electric pressure of
one volt.
In connection with these units, the prefixes of kilo, micro and milli are employed, mean-
1 1
ing respectively, 1,000 times, - - of and - - of. Thus a kilo-volt = 1,000 volts; a
1,000,000 1,000
1 1
micro-ampere — - - ampere; and a milli-volt = - - of a volt.
1,000,000 1,000
24. Current Output and Voltage of Various Devices. — For students'
information, we may review here the values of voltage and current to be expected from
various current sources and circuits in daily use. For example, primary cells of various types
generate an E. M. F. varying between 0.6 to 1.75 volts. The current output varies with the
size and nature of the elements, lying between 5 and 30 amperes for common sizes. Storage
cells generate an E. M. F. between 2.08 and 2.6 volts. The rated current output may
vary from 5 to 200 amperes, depending upon the size of the cell.
Generators or dynamos are constructed to supply potentials from 4 to 6,000 volts, the
latter value being rarely exceeded. Certain types of generators, for instance those used in
electroplating establishments, may have a current output of 10,000 amperes, with an E. M. F.
of 4 to 8 volts. The electric lighting wires of homes generally carry current at pressure of
110 volts, either direct or alternating current. Transmission lines for carrying large
amounts of power over great distances may have voltages as high as 200,000 volts, but the
strength of the current is comparatively small. The potential of trolley wires is generally
about 550 volts. Voltages in excess of 110 volts are considered dangerous to human life,
particularly those in excess of 500 volts.
Fig. lOa — Portable Wireless Transmitting and Receiving Set for Junior Military Organizations.
Note : — The physical standard for the ohm has been noted. The standard for the
strength of current is an arbitrary one. It is found that if a silver and a platinum electrode
are dipped in a neutral solution of silver nitrate (consisting of 15 parts by weight of silver
nitrate and 18 parts of water) a steady current of one ampere flowing from the silver to
the platinum will deposit .001118 grams of silver on the platinum per second.
The standard for the volt is the Weston Cadmium cell which has an electromotive force
of 1.018 volts at a temperature of 20 degrees Centigrade.
PART III.
ELECTROMAGNETIC INDUCTION.
THE DYNAMO— THE FLOW OF ALTERNATING CURRENT.
25. ELECTROMAGNETISM. 26. MAGNETIC FIELD ABOUT Two
PARALLEL CONDUCTORS. 27. THE SOLENOID. 28. INDUCED CUR-
RENTS. 29. MUTUAL INDUCTION. 30. SELF-INDUCTION.
31. VALUE OF INDUCED E. M. F. 32. THE DYNAMO. 33. DE-
TERMINATION OP FREQUENCY. 34. STRENGTH OF MAGNETIC
FIELD. 35. DIAGRAM OF AN ALTERNATING CURRENT DYNAMO.
36. DIRECT CURRENT DYNAMO. 37. SHUNT, SERIES AND COM-
POUND WOUND DYNAMOS. 38. THE ELECTRIC MOTOR. 39. THE
EFFECT OF COUNTER ELECTROMOTOR FORCE. 40. MOTOR WITH
DIFFERENTIAL FIELD WINDING. 41. DYNAMO AND MOTOR ARMA-
TURES. 42. DEVELOPMENT OF ARMATURE WINDINGS. 43. THE
ALTERNATING CURRENT TRANSFORMER. 44. ELECTROSTATIC CA-
PACITY. 45. REACTANCE AND IMPEDANCE. 46. CAPACITY RE-
ACTANCE. 47. LAG AND LEAD OF ALTERNATING CURRENT. 48. EF-
FECTIVE VALUE OF ALTERNATING E. M. F. AND CURRENT.
49. MEASURING INSTRUMENTS OR ELECTRIC METERS. 50. INDUC-
TION COIL. 51. PRACTICAL ELECTRIC CIRCUITS.
25. Electromagnetism. An explanation of some of the more important
phenomena surrounding a current carrying conductor follows : If a conductor
through which a current of electricity
_ is passing is laid parallel to and above
1 a compass needle as in Fig. 11, the
needle will tend to turn at a right
angle to the conductor, but if the cur-
rent is turned off, the needle will re-
turn to its original position. As we
have previously mentioned a magnet
suspended freely will tend to lie
parallel to a given magnetic field,
hence, it follows from this experi-
Fig. 11 — Deflection of Compass Needle by Electric , n r ,1
Current. meiit that the flow of current through
the wire of (Fig. 11) must have set
up a magnetic field and the direction of which is evidently at right angles to the
conductor. j
// the current in a horizontal conductor is flowing towards the north, and a
compass is placed under the wire, the north pole of the needle will be deflected
towards the west; if the compass is placed over the zvire, the north pole of the
needle will be deflected towards the east. Or, if the current is reversed in the
conductor, the needle will point in the opposite direction in each case respectively.
From this and other experiments we deduce that if the current in a conductor is
flowing away from the reader, as in Fig. 12a, the direction of the lines of force
will be around the conductor in the direction of the hands of a clock. If, on the
other hand, the current flows towards the reader as in Fig. 12b, the direction of
the lines of force will be around the conductor in the direction opposite to the
movement of the hands of a clock or counter clockwise.
ELECTROMAGNETIC INDUCTION.
17
26. Magnetic Field About Two Parallel Conductors. — The magnetic fields
of two parallel conductors are either mutually attractive or repellent, according
to the direction of the current in
each.
In the diagram, Fig. 13, the current
in the left hand wire is flowing away
from the reader, but in the right hand
wire towards the reader. Since the gen-
eral direction of the lines of force is op-
posite in either wire, their magnetic
fields are in opposition or in repulsion.
In the diagram, Fig. 14, current is as-
sumed to be flowing in both wires in the
same direction and since the lines of force
have the same general direction, they
combine and coalesce as shown by the
outer lines.
27. The Solenoid. — If a number
of turns of wire be wound in a
spiral, as in Fig. 15, the lines of
force generated by each turn of
wire will unite with those set up by
adjacent turns. The lines of force
inside each turn will have the same
general direction, forming several
long lines of force that may be said
to pass through the entire helix.
These lines pass out of the coil at one
end and enter at the other end, just
as in the case of the bar magnet
described in Part 1.
If the general direction of the
lines of force inside this coil is from
right to left, the left hand end will
be a north pole, the opposite end, a
south pole. The polarity of the coil
may always be determined if the di-
rection of the current is known.
The rule is that if in looking at the
end of the coil, the current flows around its turns clockwise, the end nearest to the
observer will be a south pole, but if the current flows in the opposite direction, it
will be a north pole.
A helix consisting of a number of turns through which current flows is known
as a solenoid. We see from the foregoing that a solenoid has north and south
poles and, in fact, possesses all the properties of a permanent steel magnet with
the advantage that the magnetism in the case of the solenoid is entirely under
control.
The strength of the magnetic field of a solenoid is proportional to the strength
of the electric current passing through it and the number of turns of wire com-
posing the coil, but the magnetizing power may be increased from 200 to 2,000
times by merely inserting an iron core or bar of soft iron within it.
In order that the phenomena of electromagnetic induction to be explained later
may be better understood, the expansion and contraction of the magnetic field
around a current carrying coil should be considered. // direct current of unvary-
ing strength Hows through the solenoid, the lines of force stand still when the
now of current is fully established. If the rate of How of current is increased or
decreased the lines of force increase or decrease accordingly, -or stated in another
Fig. 12a — Showing Lines of Force Around a Conductor
with the Current Flowing Away from Reader.
18
PRACTICAL WIRELESS TELEGRAPHY.
way, when the current rises, the lines of force move away from the wire but
when the current falls, the lines of force collapse back upon the wire.
The general direction of the magnetic
field around a horse shoe magnet is shown
in Fig. 16. If the direction of the flow of
current from the battery around the convolu-
tions of the two coils is as indicated, the
left hand pole has north magnetism and the
right hand pole has south magnetism. A
piece of soft iron A placed near to the tips
of the poles will be forcibly drawn to them
and will only be released when the current
is turned off. If a coil of resistance wire
R, such as a German silver resistance regu-
lator, is connected in series with the wind-
ings, the strength of the magnetic field can
be closely regulated. If high values of re-
sistance are inserted, the current may be re-
duced to a degree that the magnet will barely
attract the piece A. Variation of the cur-
rent flow would affect the field of a straight
solenoid winding in the same manner. The
point to be taken from this is that whenever
electromagnets are employed for mechanical
work such as lifting masses of iron or for
exciting the magnets of a dynamo or motor,
the strength of the field can be regulated
over certain limits by a simple variable re-
sistance.
If a horse shoe of hard tempered steel be
inserted in the magnetic windings in place
of the soft iron core and allowed to remain
for a few seconds, upon removal it will be
found to be permanently magnetized.
We have explained that the direction of
the magnetic field around a conductor de-
pends upon the direction of the flow of cur-
rent. It is clear that if the current of the
magnet in Fig. 16 is reversed the polarity
will be reversed as shown in Fig. 17.
The strength of the magnetic field
about a solenoid can be varied by
fluxes of opposite directions as shown in Fig. 18. The solenoid windings
A and B are wound in opposite directions connected in series and finally
to the terminals of the battery. Since current flows through the two coils in
opposite directions their magnetic fields are repellent and if the coils are
telescoped together (one within the other) the magnetic field will be nearly
destroyed. If the two coils are partially telescoped, the resultant magnetic field
varies accordingly. Advantage is
taken of this principle in construct-
ing an instrument known as the
variometer, which is particularly
useful for tuning wireless telegraph
circuits.
The electromagnet in some form is
employed in nearly all electrical ma-
chinery, and, therefore, the laws r
J .' r i « til Fig. 13— Lines of Force About Two Conductors Carrying
governing magnetic fields Should Current in Opposite Directions,
Fig. 12h — Showing Lines of Force Around a Con
ductor with Current Flowing Towards Reader.
ELECTROMAGNETIC INDUCTION.
19
have careful attention. Study of the phenomenon of magnetic induction is par-
ticularly important as it is encountered at many points in a wireless telegraph set.
28. Induced Currents. — We have already seen that a magnetic field in-
variably accompanies the flow of electricity
through a conductor and conversely we find
that whenever a conductor is moved
through a magnetic field, an electromotive
force will be induced therein, and a flow of
current will take place if the conductor
forms a closed or continuous circuit. This
is the fundamental principle upon which
the operation of the dynamo or generator
is based.
Experiment reveals that the production
Fig. 14 — Lines of Force Around Two Conductors of the E. M. F. is conditioned by the fol-
lowing rule: The motion of the coil must
take place in such a way as to change the total number of magnetic lines of force which
are enclosed by the coil.
Eor instance, simply moving a coil in a uniform field from one position to another, so
that the lines of force enclosed by the coil remain of constant number, will not induce a
flow of current, but if the coil is rotated, for example, so that the lines of force enclosed by
it either increase or diminish, an E. M. E. will be induced which varies according to the
rate at which the lines of force change.
The induction of current by a magnetic field threading in and out of a coil can be
shown by a simple experiment. If the terminals of a solenoid wound with fine wire are
connected to a current indicating device, such as a galvanometer, and a permanent bar
magnet plunged into the interior of the winding, a momentary deflection of the galvanometer
is observed. If the bar remains within the coil there is no further movement of the current
indicator. If the bar be suddenly withdrawn, the galvanometer gives a second deflection in
the direction opposite to that cited in the first instance. This experiment proves that the
cutting of the flux through a coil of wire induces a current therein and that the direction
of the current reverses with the flux. Currents will be induced in the coil if it remains
stationary and the magnetic flux passes in and out of the coil, or if the field is stationary
and the coil is moved through it. In either case, an E. M. F. is generated proportional to
the rate at which the conductor cuts through the field.
We may substitute for the bar magnet just mentioned a solenoid winding P and cause
its magnetic field to act upon a second winding S as in Fig. 19. When the circuit of wind-
ing P is opened at key K, no lines of force are in evidence, but at the moment the key is
closed, the lines of force expand from the core P and intersect or cut through the winding
S. The galvanometer then gives a momentary deflection. If the current is left to flow
through P, there is no further effect in S until the circuit of P is opened by the key; the
galvanometer now gives a second momentary deflection but the needle moves in the opposite
direction just as in the case of the bar magnet. Thus for each "make" and "break" of the
first circuit, two pulses of current flow through the winding S, the first in one direction
around the circuit, and the second in the op-
posite direction. This current is said to be
induced in S by electromagnetic induction.
29. Mutual Induction. — It is of
great importance to note that the effect in
S takes place only when the circuit of P
is made and broken. When current is
flowing in P continuously, the magnetic
lines of force are stationary, and conse- / i-
t ,'"'
I I
quently current is not induced in S. But
when the lines of force about S rise and \
fall, then there will be a movement of cur-
rent through S. If the winding S is placed
at a right angle to P instead of lying paral-
lel to it, a change of flux in P will have
little or no effect upon S.
V
Fig. 15 — Magnetic Field of Solenoid Winding.
20
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 16 — Magnetic Field of Horse-shoe Magnet with
Current Flowing in Definite Directions.
HIM
Fig. 17 — Showing How Magnetic Field Reverses
with Reversal of Current.
The direction of the current induced in
S should be observed. When the lines of
force increase through S, the induced pres-
sure is counter to that which originally
flowed in winding P, but when the lines
of force decrease through S, the induced
current has the same direction as the orig-
inal current from the battery through
winding P.
It is clear that the lines of force in S
are in the opposite direction to those which
set up the current in S. The field of force
created around S therefore reacts upon
winding P tending to build up a current
in opposition to that already flowing in P.
That is, the change in strength of the
primary current in P induces a secondary
current in S which in turn induces a back
pressure in P. The induction due to the
two circuits reacting upon each other
is called their mutual induction which is a
measurable quantity.
30. Self-induction. — We have
seen that the expanding field of wind-
ing P induces an electromotive force
in winding S. Similarly the field
produced by each turn in winding P
will cut neighboring turns, thereby in-
ducing in them electromotive forces
that tend to oppose the E. M. F. of
the original current. On the other
hand, when the current in winding P
diminishes, the lines of force contract
and thereby induce electromotive
forces in adjacent turns, that tend to
set up currents in the same direction
as the original current.
This inductive action of a coil or
conductor upon itself is called self-
induction.
Self-induction may be defined as
the property of a circuit that tends to
prevent any change in the strength of
currQnt passing through it. This is
clear from the fact that self-induced
currents either tend to prevent the
rise or the fall of current through a
circuit.
The effects of self-induction are
noticeable only in direct current cir-
cuits when the current is turned on
and off, but in alternating current cir-
cuits they are ever present. All con-
ductors have self-induction. the
amount depending upon their size and
shape. Coiled wires have greater
self-induction than a long straight
wire. The self-induction of a coil
ELECTROMAGNETIC INDUCTION.
21
without an iron core is practically
constant. If a given coil has an iron
core, the self-induction is greater in
proportion to the permeability* of the
iron.
The coefficient of self-induction or
inductance is also defined as the prop-
erty of a conductor by which energy
may be stored up in magnetic form.
The unit of inductance is the
henry and represents the cutting of 100,000,000 lines of force when one ampere
of current is turned on and off per second ; that is, if one ampere is turned on and
off, in a given conductor, the electromotive force induced by the collapse of the
magnetic field, equals one volt.
Fig.
k
18 — Variation of Magnetic Field by Opposing
Coils.
Fig. 19 — Diagram Illustrating the Principle of Electromagnetic Induction.
This means that a conductor or coil to have self-induction of one henry must be of such
length and shape that when one ampere is flowing it is surrounded by 100,000,000 lines of
force, and when the current is turned on and off, 100,000,000 lines of force cut through the
conductor setting up a pressure of one volt.
This can be expressed :
M X T
L-
I X 100,000,000
where T = the total number of turns in a given coil;
M = the total lines of force threading through the coil ;
and I = the current in amperes.
If M = the lines of force threading through the coil when the current = 1 ampere, then
M X T
L =
100,000,000
The unit, the henry, is applicable to coils of a great numlDer of turns having iron cores, but
for coils encountered in wireless telegraph transmitters, some sub-multiple of the henry is
desirable, such as the micro-henry, the milli-henry and the centimeter.
* Permeability is a measure cf the ability of a magnetic substance to conduct magnetic lines of force.
22
PRACTICAL WIRELESS TELEGRAPHY.
1,000 centimeters = 1 micro-henry;
1
1 micro-henry =.— —henry;
1,000,000
1
1 rmlli-henry —
henry;
1,000
The inductance of a given circuit is generally calculated by one of several formulae.
31. Value of Induced E. M. F. — Referring- to Fig. 19: The electromotive
force induced in winding S is conditioned on the ratio of the turns in the two windings
and the rate of the change of flux threading through S. For instance, if P has 100 turns
of comparatively coarse wire such as No. 14 or No. 16 B. & S. wound over an iron core
and S has many thousand turns of fine wire such as No. 36 B. & S., an electromotive force
of several hundred thousand volts may be induced in S. Should winding S have less turns
than winding P, the E. M. F. induced in S will be lower than that of winding P. Ad-
vantage of this principle is taken in the design of the apparatus known as the induction
coil, in which the circuit of P is interrupted from thirty to one hundred times per second.
Then if winding S is given a large number of turns and its terminals are separated by a
space of several inches, the voltage may be so great as to jump the gap in the form of an
electric spark.
To properly distinguish the various circuits, winding P is called the primary; winding S
the secondary winding. The current in P is termed the primary current and in S the
secondary current.
Fig. 20 — Fundamental Diagram of Simple Alternator.
32. The Dynamo. — We may briefly define the dynamo as a machine for
converting mechanical energy into electrical energy by the principle of electro-
magnetic induction. But unlike the simple battery or storage cell the dynamo
may generate either direct or alternating current. Alternating current dynamos
are frequently called alternators. The student can nearly always distinguish
between the two machines by observing the part of the dynamo at, which the
current is collected. If the brushes rest on a commutator made up of a number
of copper segments separated by insulating material, it will be a direct current
dynamo, but if the brushes simply rest on two brass rings, it will be an alternating
current dynamo.
The fundamental principle of the dynamo follows : Whenever a coil of wire
rotates through a magnetic field of uniform strength in such a way that the
ELECTROMAGNETIC INDUCTION.
23
number of lines of force enclosed by the coil increase or diminish uniformly, a
current of electricity will be induced in the coil, the strength of which at any
instant is proportional to the rate of the change of flux.
Hence the essentials of a dynamo are :
(1) A magnetic field of constant strength;
(2) A number of coils mounted on a shaft and rotated in such a way as to cut
through the magnetic field;
(3) Means for conducting the current induced in the rotating coils to an outside
circuit.
A diagram of an elementary alternator appears in Fig. 20. A uniform magnetic field is
set up between the magnetic poles N and S by the current from battery B-l which flows
through the magnet windings M, M. The rectangle of wire A, B is mounted on a shaft
which rotates clockwise. Two brass rings, C, D, are mounted on the shaft but insulated
from it. The copper brushes H and L make contact with these rings, and the circuit is
completed through F (any current absorbing apparatus).
According to the principle just explained, if A, B rotates around its axis, an E. M. F.
will be induced in the loop, the magnitude of which depends on the rate of charge of the
number of lines of force threading through the loop. When in the vertical position of Fig.
20, the loop encloses the maximum number of lines of force, but when side A goes under-
neath the S pole and side B goes under-
neath the end pole, as in Fig. 21, the rect-
angle will enclose the minimum number of
lines of force when it has moved 90 de-
grees or in a horizontal position. As A
moves out of the field of the south pole
and B out of the field of the north pole,
the rectangle reaches another vertical posi-
tion (but with the two sides of the rect-
angle reversed) and again encloses the
maximum number of lines of force. As
the rotation of A, B continues, side A -goes
into the field of the N pole and side B
goes into the field of the S pole, where
for a second time the minimum number
of lines of force are enclosed after which
the loop returns to the position mentioned
at the beginning.
Now, according to the rule which gov-
erns the direction of the flow of current in
a conductor cutting through a magnetic
field, when A, B, is in the position of Fig.
Fig. 21 — Showing Position of Armature Conductors for
Maximum Cutting.
21, a current will flow towards the rear of the rectangle in the left hand side, and towards
the front of the rectangle on the right hand side. Then if A, B, continues y2 revolution,
so that side A is cutting through the N field and side B through the S* field, current will
flow in A, B, in the opposite direction. It is clear that in a complete revolution, A, B,
undergoes two changes of current which flows first in one direction around the rectangle
and then in the opposite direction. The current is said to have gone through a complete
cycle.
We see that during the first quarter revolution of loop A, B, or from 0° to 90°, the
E. M. F. increases from zero to maximum; from 90° to 180° the E. M. F. decreases from
maximum to zero; from 180° to 270° the current reverses and the E. M. F. increases from
zero to maximum, and from 270° to 360° the E. M. F. again decreases from maximum to
zero.
The changes in the strength of the current induced in A, B, can be shown by a wave-like
curve as in Fig. 22, in which the successive positions of the rectangle are shown by the
positions, 1, 2, 3, 4, 5, 6, 7, 8, etc. From position 8-16 the E. M. F. gradually rises, maximum
E. M. F. being attained in position 4-12. This increase of E. M. F. is indicated by the
ascending slope of the curve B to C. From position 4-12 on, the E. M. F. decreases (as
indicated by the descending slope of the curve B to C), the minimum cutting of the lines
of force taking place at point 8-16. This corresponds to the point X1 on the horizontal line.
As the rectangle continues the revolution, the lines of force are cut on an increasing angle,
another maximum of E. M. F. being attained at point 12-4, but of the opposite sign as
24
PRACTICAL WIRELESS TELEGRAPHY.
shown at point D. From, this point the E. M. F. decreases to zero or when the rectangle
A, B, is in the position of 16-8. This curve depicts the gradual rise and fall of the E. M. F.
in a dynamo coil and is known as a sine curve, the plotting of which is explained in the
principles of co-ordinate geometry. The curve shows the relation between time (fractions
of a second) and the strength or amplitude of the current at any given point during the
complete revolution of a dynamo coil. The curve represents a complete cycle of alternating
current. Vertical lines drawn from the horizontal A, B, represent time in fractions of a
second. The horizontal lines drawn from the successive positions of the coil, 1, 2, 3, 4, etc.,
correspond to the position of the dynamo coil at any particular instant. At points where
the horizontal and vertical lines intersect, a common line is drawn connecting them, which
results in the wave-like curve.
33. Determination of Frequency. — The frequency of an alternating cur-
rent dynamo is expressed in cycles per second. We see from the previous para-
graph that one complete cycle of current is generated when A, B, makes a single
revolution. Hence if A, B, rotates 60 complete revolutions per second, there will
be 120 reversals or alternations of current per second. Since two alternations of
IN CASE OF 500 CYCLE ALTERNATOR
Fig. 22 — Sine Curve Showing Rise and Fall of Current during One Complete Cycle.
current constitute a complete cycle, the frequency of this generator is said to be 60
cycles.
The frequency of any alternator may be determined by first counting the
number of field poles and by measuring the speed of the armature per second of
time, or
N X S
Frequency =
v 2
Where N = the number of field poles ;
S = the speed of the armature in revolutions per second.
Direct reading frequency meters are in daily use. They are connected in
shunt to the power circuit like the voltmeter. (Frequency meter is described in
Paragraph 49, section C.)
34. Strength of Magnetic Field. — The strength of the magnetic field about
the poles N and S, Fig. 20, is proportional to the strength of the current in amperes and the
number of turns of the coil. The strength of the magnetic field Is the same whether a
current of a large number of amperes is flowing through a few turns 6f wire or a relatively
weak current flows through a greater number of turns. The turns of the field winding
of any dynamo are of a fixed number ; hence the strength of the magnetic field is regulated
by increase or decrease in the strength of the current flowing through tthe field winding.
ELECTROMAGNETIC INDUCTION.
25
The field current is regulated by a device known as a field rheostat which is simply a
variable resistance connected in series with the circuit.
The voltage developed in any given dynamo coil is proportional to the rate of cutting
of the magnetic field. In the case of the rectangle A, B, of Fig. 20 or 21, the total flux
passes in the coil twice and out twice during one revolution or during one cycle. If the
coil enclosed 100,000,000 lines of force and made one complete revolution per second,
100,000,000 lines of force would be thrust into the coil twice and thrust out twice. This
would be the equivalent of cutting 400,000,'OOQ lines of force per second and in this
particular case the induced E. M. F. would be 4 volts. If the number of turns on the
armature winding were doubled, all other conditions remaining equal, the voltage would
1 10 VOLT D.C.
FIELD POLE
IIOVOLTS
60-500
CYCLES
-O-
-O-
LQAD
Fig. 23 — Fundamental Diagram of 4 Pole A. C. Generator.
be double, or we might state that if there were N turns, the E. M. F. developed would
be N X that of 1 turn.
The fundamental equation for the dynamo is :
4XNXnXS
E —
100,000,000 X P
Where E = the average voltage of the dynamo ;
n = the revolutions of the armature per second ;
N — the number of conductors on the surface of the armature ;
P = the number of pairs of poles ;
S = the total number of lines of force.
In a commercial dynamo, the only factors in this equation which are variable,
26
PRACTICAL WIRELESS TELEGRAPHY.
are (1) the density of the magnetic field and (2) the speed of the dynamo arma-
ture per second. We see from this that the voltage of any generator may be
increased by increase of the speed of the armature or by increase of the strength
of the magnetic field surrounding the armature coils. Commercial generators are
built usually for constant speed. Regulation of the voltage is obtained by means
of the field rheostat.
35. Diagram of an Alternating Current Dynamo. — The essential parts of
an alterating current dynamo are :
(1) Field Magnets.
(2) Armature.
(3) Collector Rings.
The diagram of Fig. 23 is merely intended to show the general details of the
construction and connections of an alternating current dynamo. The field poles
which are firmly bolted to the circular iron frame are represented by N, S, N, S,
the armature at M and the collector rings at E, F. The field poles are wound
alternately in opposite directions so that the current circulates about the turns in
opposite directions, giving the poles alternatively north and south polarity. The
armature M is built up of a number of slotted sheets of soft iron which are pinned
together and mounted on a common shaft, the copper conductors lying lengthwise
of the core in such a way that the coils will be filled and emptied with magnetic
flux (coils not shown). If these coils are properly connected together, the
currents induced therein (by the change of flux) will flow in the same gen-
eral direction, the voltage of one coil being added on to that of the next coil.
It is to be especially noted that the source of continuous or direct current for
exciting the field poles of an alternator is generally supplied from an external
source which may be either a small direct current dynamo known as an exciter
or a battery of storage cells. In most cases encountered in wireless working, the
pressure of the direct current source is 110 volts and the number of the turns of
the field winding are such that the correct amount of current flows with small
amounts of resistance in series at the rheostat R. As already explained, this
resistance is known as the field rheostat or field regulator.
When the armature M revolves at a uniform rate, an alternating current is induced in
the coils which is collected by the brushes E, F in contact with 2 collector rings, the volt-
tage varying with the design of the machine. For purposes of wireless telegraphy the
voltage of the generator may vary from 110 to 500 volts and the frequency of the current
may vary from 60 to 500 cycles standard frequencies being 60, 120, 240 and 500 cycles.
If the armature of Fig. 23 were revolved 1800 revolutions per minute, current at a
frequency of 60 cycles per second would be obtained from its armature. Remembering the
formula given for determining the frequency we see that in a complete revolution of the
armature any point passes through four fields which would set up four reversals of current.
If the armature revolves at the rate of
1800 revolutions per minute, corresponding
to 30 revolutions per second, there would
be a 4 X 30 or 120 reversals of current,
or a frequency of 60 cycles. If the genera-
tor had 32 field poles, the frequency would
be 32 X 30 or 960 alternations correspond-
ing to 480 cycles.
The student should understand that the
foregoing description and drawing simply
shows in an elementary way the construc-
tion and functioning of a generator. The
diagram is merely intended to indicate the
connections of the machine, the direction
of the magnetic lines of force and the
method by which the voltage generated by
Fig. 24.— Showing the Function of a Simple Commutator, the armature is regulated.
ELECTROMAGNETIC INDUCTION.
27
36. Direct Current Dynamo. — Direct current is obtained from dynamo coils
by a commutator, which is placed on one end of the armature driving shaft. In
simple form it consists of a split brass or copper ring of two parts, C, D, which
is thoroughly insulated from the armature shaft (shown in Fig. 24). The circuit
from the loop A, B is completed through the contact brushes E and F through
an external load as at R.
The function of the commutator should be clear from the following explanation : As-
sume the coil A, B to be in rotation in the direction of the arrow ; then in the particular
position shown in Fig. 24, the segment D will be a (-f ) pole and segment E a ( — ) pole.
The current will therefore flow in the external circuit from brush F to brush E. When
A, B turns completely over so that side B goes under the south pole and side E under the
north pole, the current will flow in B as it did formerly in side A, that is, towards the
brush F. Similarly, when A is in the north field, the current will flow away from brush
E. Therefore, the current will flow in the external circuit in the same direction as in the
first case.
We see also that in the second position mentioned, the current in B is flowing oppositely
to that when B was cutting through the north field, but we must keep in mind that com-
mutator segment B now makes contact with brush F instead of brush E. Thus the cur-
rent will flow in one direction in the external circuit irrespective of the rate at which A, B
revolves.
A steady flow of current like that obtained from a battery of chemical cells cannot be
obtained from the dynamo; the latter in reality generates a pulsating current. If the dynamo
armature is composed of a great number of coils, the pulsations are so minute and follow
each other so rapidly that the current is practically continuous. That is, these pulsations
are made to overlap one another by mounting a number of loops of the armature and
connecting them in series so that immediately one set of coils passes the position of
maximum cutting of the lines of force, another set will take their place. The greater the
number of the armature coils the greater will be the number of commutator segments
required. In fact, commutators in commercial dynamos may have from 50 to 150 segments
depending upon the design of the dynamo.
37. Shunt, Series, and Compound Wound Dynamos. — We have already
explained that continuous or direct current must flow through the field windings
of an alternating current dynamo and that this current is obtained from an
external source. In the direct current dynamo, the current for excitation of the
field is obtained from its own armature.
When the terminals of the field winding are tapped across the brushes of a direct cur-
rent dynamo, it is called a shunt wound dynamo. The circuit for this machine is shown in
the diagram, Fig. 25, where the terminals of the field winding are tapped across the arma-
ture circuit at points C and D. A regulating rheostat connected in series with the field
circuit at R permits an increase or decrease of the strength of the current flowing. The
field winding of the shunt dynamo is composed of a large number of turns of com-
paratively fine insulated wire, the actual
number of turns being governed by the
flux required, whereas the armature coils
have comparatively coarse wire. Two
paths are presented to the current as it
flows from the armature of this machine,
one being the field circuit and the other,
the external circuit.
In well designed shunt dynamos, the re-
sistance of the shunt circuit is always
greater than the resistance of the armature
and external circuit, but the strength of the
current flowing in the shunt coil is in fact
comparatively small even in the larger types
of generators.
The student may question how current
is set up in a machine of this type when it
is first put into motion. The fact is that the
initial building of the current is due to
residual magnetism in the field cores. When Fl>. 25-Circuit of Shunt Wound D. C. Generator.
28
PRACTICAL WIRELESS TELEGRAPHY.
FIELD
ARMATURE
a piece of soft iron has been magnetized, no matter how soft the iron may be, a certain num-
ber of magnetic lines of force are retained when the magnetizing current has been turned
off. These lines are known as the residual lines of force and the cores of the field winding
are said to possess residual magnetism.
When the dynamo armature is first set into rotation, the residual lines of force pass in
and out of the armature conductors through the core, generating therein a feeble current
which flows to the field winding and increases the number of lines of force threading through
the armature coils. This induces a stronger current in the armature conductors which con-
tinually adds to the strength of field until the normal voltage of the dynamo is established.
The complete process usually requires from 10 to 50 seconds. After the generator armature
attains its normal speed, the voltage across its terminals may be raised or lowered by the
rheostat R. If the resistance of R is increased, the voltage diminishes, or if the resistance
of R is decreased, the voltage increases.
A diagram of a series wound generator appears in Fig. 26. The field magnets
of this type are wound with a few turns of thick wire joined in series with the
armature brushes and all of the cur-
rent generated by the armature passes
through the coils of the field magnet
to the external circuit. The current in
passing through the windings of the
field magnet, energizes them and
strengthens the weak field due to the
residual magnetism of the cores which
results in a gradual building up of the
magnetic field. The important char-
acteristic of this machine is its ability
to furnish current at increased voltage
as the load increases for it is clear from
previous explanations that the greater
the strength of the field current, the
greater the strength of the magnetic
field from pole to pple. The strength
of the field current flowing through a
series wound generator, and therefore
the voltage across its armature is reg-
ulated by cutting out turns of the field
lerator. through the medium of a multi-point
switch or as may be done in the case of any type of generator, the voltage can be
regulated by variation of the speed of the armature.
The compound wound dynamo combines the desirable characteristics of both
the series and shunt wound machine, and it gives a better regulation of voltage
on circuits of varying load than is possible with a dynamo of either type. A
suitable diagram of connections appears in Fig. 27. The field magnets of the
compound dynamo are wound with two sets of coils, one set being connected in
series with the armature as shown at R, and another set in shunt to the armature
and external circuit as shown at V. The function of the series winding is to
strengthen the magnetic field by the current taken through the external circuit,
and thus automatically sustain the voltage under variation of a load.
In the case of the shunt wound dynamo, as the external load is increased, the potential
difference at the armature terminals will fall, but in the case of the compound wound gen-
erator, this fall of pressure is counteracted by the series winding, the current which flows
in it increasing with the load and causing the pressure to rise. The number of turns of each
winding and the relative strength of current is proportioned so that a practically constant
pressure is maintained under varying load. Initial adjustments of the voltage can of course
be secured by means of a field rheostat such as shown at R-l.
The student should note carefully that current must circulate in both the
ELECTROMAGNETIC INDUCTION.
29
series and shunt windings in the same general direction in order that the re-
sultant magnetic fields may have the same general direction.
38. The Electric Motor.— A motor is a machine for converting electrical
energy into mechanical energy. There is essentially no difference between a
motor and a dynamo. Any dynamo connected to a source of electric power will
run as a motor and any motor driven by mechanical power such as a steam
engine, etc., will generate a current of electricity. The differences between the
two machines are mainly mechanical.
The fundamental operating principle of
the motor is as follows: A wire carrying
a current placed in a magnetic field will
tend to move in a direction at right angles
both to the direction of the field and to the
direction of the current. For example, if
the plane of a given coil of wire lying be-
tween the poles of a magnet is parallel to
a magnetic field, and a current is passed
through the coil, it will tend to turn or
to take up a position at a right angle to the
magnetic field. If the current is reversed
when it has reached this position, the coil
will continue to revolve.
The action of the motor can be simply
explained by the diagram of Fig. 28 where
a motor armature, commutator and brushes
as well as the field poles, are represented
in a conventional manner. If the terminals
G, H, be connected to a source of direct
current, part of the current will circulate
through the field windings and part through
the coils of the armature between the two
brushes. If the current flowing through Fig. 27— Circuit of Compound Wound D. C. Generator,
the armature coils bears the correct direction to that flowing through the field winding, a
state of magnetism such as shown in Fig. 28 may be produced. The upper half of the arma-
ture core above the imaginary line X, will be a south pole and the lower half a north pole.
The lower half of the armature will then be attracted by the south field pole and repelled by
the north field pole and the upper half will be repelled by the south field pole and attracted
by the north field pole. This may be stated in another way by stating that the coils of the
armature tend to turn until they enclose the greatest number of lines of force from the field
poles. The general strain of this attraction and repulsion is seen to be clockwise.
The movement of the armature will be continuous because the commutator acts to main-
tain in the same direction the flow of current through the two sides of the armature always.
Consequently, the upper half of the armature will always be a south pole while the lower
half will be a north pole, irrespective of the speed at which the armature revolves.
Now it would have no effect on the general direction of rotation if the connections from
the source of current to the motor were
reversed because the polarity of the flux
in both the armature and the field poles
would be reversed accordingly and be-
cause the strain of the two magnetic fields
would have the same general direction
the motor would revolve in the same di-
rection as before. Careful consideration
of this fact reveals that in order to
change the direction of rotation of the
armature, the flow of current must be
reversed independently in either the
armature or field poles.
Like generators, motors may have
series, shunt, or compound wind-
110 VOLT O.C.
Fi6'
d
30
PRACTICAL WIRELESS TELEGRAPHY.
ings. The type known as the differential wound motor appears in Fig. 29 and will be
described further on.
39. The Effect of Counter Electromotive Force. — When a motor armature
is set into motion by an external current, the loops of wire composing its coils cut through
the magnetic field and induce a reverse electromotive force counter to that which originally
caused the motion. This back pressure is known as counter electromotive force which gov-
erns directly the speed of a motor. The difference between the impressed and the counter
voltage determines the actual flow of current in the armature and the counter voltage is
proportional to the speed of the armature, the number of armature wires and the strength
of the magnetic field which is enclosed.
The speed of a motor supplied with current at constant pressure varies directly with the
counter electromotive force and in any given machine the stronger the field, the slower will
be the speed of the armature. If the field
of a motor be weakened by inserting re-
sistance in the excitation circuit, the
armature will increase its speed up to a
certain point, or until the increased speed
of the armature increases the counter
E. M. F. to such an extent as to cut down
the armature current. Up to this point,
however, the speed of any given motor
can be varied by simply increasing or de-
creasing the field strength.
The pull* of the motor armature is di-
rectly proportional to the strength of the
armature current and to the strength of
the magnetic field. In the case of the
shunt wound motor where the field is of
constant strength, the pull of the arma-
ture depends upon the- amount of current
through its winding. Hence if we weaken
the field, the reduced counter E. M. F. will
permit increased flow of current in the
armature, and therefore, will increase its
speed.
The speed of a shunt wound motor is
self-adjusted in the following manner: If a load is thrown on suddenly, the armature will
have a tendency to slow down, but this decreases the reverse electromotive force and there-
fore increases the current flowing through the armature winding. This causes the motor to
return to its normal speed of rotation.
We see from the foregoing that the speed of a motor can be regulated in two
ways : ( 1 ) by connecting a variable resistance coil known as a field rheostat in
series with the field winding; (2) by connecting a variable resistance of large
current-carrying capacity in series with the external circuit or in series with the
circuit to the armature itself.
The motors of the motor generators used in wireless telegraphy are designed
to permit variation of the speed 20% above and below the normal speed.
40. Motor with Differential Field Winding. — As we have explained, the
speed of a motor is increased or decreased by regulation of the strength of the
magnetic field and any reduction of field flux of a given machine will increase
the speed of the armature. By the use of the differential field winding shown in
Fig. 29, the flux of the shunt field is automatically weakened in accordance with
the external load and the speed therefore self-regulated. Confining our vision
strictly to the windings of the field poles, two distinct set of coils will be seen,
one a series winding (SR) in series with the armature and the other a shunt
winding (SH) connected across the main power line. If the current in these
two windings circulates in opposite directions, a differential field is produced
and the resultant field will be of greater or less intensity according to the current
*The term "torque" is applied to the twisting force produced in the armature when the current
is turned on. "Torque" is the result of "pull" and "leverage."
110 VOLT D.C
Fig. 29— Motor with Differential Field Winding.
ELECTROMAGNETIC INDUCTION.
31
taken by the armature. A suddenly applied load will tend to slow the armature
down, and this will reduce the counter E. M. F. of the armature coils ; accord-
ingly increased current will flow through the series winding, which will reduce
the counter E. M. F. to a still lower figure, permitting such increase of armature
current as will restore the motor to normal speed.
Through use of the differential winding motors may be designed to give
very close speed regulation and are therefore distinctly suitable to drive the A. C.
generators for wireless telegraphy.
If we keep before us the fact that the counter electromotive force developed
in a motor armature acts effectively as a resistance to the flow of current, and
that this reverse electromotive force increases with the speed, it is easily seen
that a considerable difference must exist between the armature resistance when
standing still and its effective resistance when in rotation. If such a motor
armature were started by connecting its terminals directly to the power mains
an excessive current would flow which would do injury to the windings or the
commutator. A device known as a motor starter is, therefore required to reduce
the starting current to a safe value.
Motor starters will be treated in detail in Part IV7, paragraphs 55, 56 and 57.
41. Dynamo and Motor Armatures. — Armatures may be classified with
A particular reference to their shapes, the
r \ t \ two principal types being known as the
I El_UIIIIIII!lllllllllllllllinilllllllllllllllllll^ Tr'd,?gram,aFidg.1of
outline of the drum wound armature, the
A »• V I || I/ core of which is made up of a number of
Nlllllllllllllllllllllllllllllllllllllllllllllllllllllly thin sheets of soft iron mounted on the
* ' shaft B to form the support for armature
Fig. 30-Gencral Outline of Drum Wound Armature. coils The coUs f()r ^ armature arc
placed lengthwise in slots, one coil being shown as at A, B. One terminal, A, B, is con-
nected to a segment of the commutator and the winding continues through a slot to the
rear of the armature core underneath a south pole, and returns in the case of a four-pole
dynamo or motor about 90° away or underneath the north pole where the second terminal
is attached to the next adjacent commutator segment. A number of these coils are con-
nected in series, taps being brought from the terminals of each coil to the successive seg-
ments of the commutator. The iron punchings of the core 0 are insulated from one an-
other by shellac or varnish to prevent the induction of current in the core as well as in
the armature coils. A solid core would occasion great energy losses in this way.
An armature coil constructed of thin discs or punchings is said to be laminated. The
field poles and armatures of both dynamos and motors are laminated to prevent induction
losses.
In the ring wound armature shown in Fig. 31, the armature conductors are wound about
a ring-shaped iron core, separated from one another and equally spaced, the term-
inals of each coil being connected to ad-
jacent segments of the commutator. Be-
cause the conductors on the outside
surface of the core only are active in cut-
ting the lines of force, the ring wound
armature is more or less wasteful and is
seldom encountered in wireless telegraph
installations.
42. Development of Armature
Windings. — The subject of arma-
ture windings is too comprehensive
to be treated in detail here. These
windings are exhaustively covered
in many textbooks on dynamo engi-
neering which should be referred to
for additional details. The drum Fi 31_Gen,rai Outlin? of Ring Woun<J Armatu
32
PRACTICAL WIRELESS TELEGRAPHY.
armature windings may be classed into two principal types, the lap winding and
the wave winding.
The development of the lap winding is shown in Fig. 32, where a number of armature
coils, numbered 1, 2, 3, 4, 5, etc., successively, are assumed to be mounted on the armature
of a dynamo and to cut through the magnetic fields of the poles N. S, N. >S. The arrow
indicates the direction of rotation, and the letters correspond to the segments of the com-
mutator. The position of the positive (-f ) brush of the armature is shown.
In this diagram, an armature having 18 conductors revolves in a four pole field and the
flow of current will be observed to have the following direction. If we start from com-
mutator segment I, the point where the current enters the armature through the negative
brush, then the current flows through conductor 17, through commutator segment A,
through conductors I and 6, and out at segment B. The current is thus seen to take two
paths from the negative brush through the armature coils to the positive brush. And it
will be clear also that one side of a given armature coil lies underneath a north pole and
the opposite side underneath a south pole 90° distant. The student should note carefully
the direction of the flow of current in all coils of the armature winding, taking particular
note of the fact that in parts of the armature, the current is flowing towards the positive
brushes and in other parts, away from the negative brushes. The coils composing the
Fig. 32— Development of Lap Winding on Armature.
armature winding are connected so that the voltage induced in one adds on to that of the
next coil, hence, current flows in the same general direction through various groups of
coils although the sides of a given coil are under magnetic fields of opposite polarity.
It is to be noted that the brush shown in Fig. 32 short circuits a particular
coil of the armature, which lies in the neutral magnetic field. It is self-evident
that if a given armature coil were short circuited by a brush when the coil occu-
pies a position other than the neutral position, it would be surrounded by a mag-
netic field and current of great strength -would be induced therein. This would
overheat or melt the conductors or at least would cause destructive sparking at
the commutator.
If the armature wiring in Fig. 32 is carefully traced out, it will be observed
that the winding, so to speak, laps back upon itself. It is therefore termed the
lap winding. In a four-pole generator, four brushes would be required for this
winding and in a six-pole generator, six brushes.
In the diagram of Fig. 32 the coils of the armature are shown as consisting
of a single turn of wire but they may have several turns between segments as
ELECTROMAGNETIC INDUCTION.
33
shown in Fig. 33 where a single coil is connected to commutator segments
B and C.
Fig. 34 shows the development of the so-called wave winding. The path of the current
is as follows : Current enters commutator segment I, continuing through conductor 17,
or to segment E, continuing through conductors 9, 14, finally
coming out at segment A. The current having passed
through a conductor under each field pole, it returns to the
commutator segment A, the one adjacent to segment I, at
which it originally started. There are but two paths for the
current through the armature, hence but two contact brushes
are required. The majority of motors encountered in wire-
less work have lap wound armatures.
The general construction of a drum-wound armature is
shown in Figs. 35 and 36. Fig. 35 shows a complete Crocker-
Wheeler motor generator armature. It should be observed
that the D. C. armature coils lie lengthwise in slots on the
iron core and their terminals are soldered in slots at the end
of each commutator segment. Fig. 36 shows the terminals
of the armature coils placed in the slots ready for soldering.
The construction of the commutator should be noted. It is
_ made up of a number of copper bars separated by fiber
J insulating material.
I B I C I
COMMUTATOR
43. The Alternating Current Transformer.— We
011 have shown in paragraphs 28 and 29 how a varying
magnetic field threading in and out of a coil of wire wound over an iron core can
induce a flow of current into another coil wound about it. Mention was made of
the fact that direct current flowing through the first coil must be interrupted or
its strength changed periodically to induce a current in the second coil.
It is clear from Fig. 19, that the lines of force produced by winding P cut each
turn in S just once, and, therefore, the pressure or electromotive force induced
Fig. 34 — Development of Wave Winding.
in winding S increases or decreases accordingly as the number of turns in S are
greater or less than in P (see paragraph 31).
The apparatus built upon this principle is known as a transformer and the
different types are called step-up or step-down with respect to the ratio of the
primary and secondary turns.
34
PRACTICAL WIRELESS TELEGRAPHY.
The essentials of a transformer are:
(1) A primary winding;
(2) A secondary winding;
(3) An iron core.
In order that the current may be induced in the secondary of a transformer, the
primary winding must be traversed by either a pulsating or interrupted direct current
or an alternating current.
Fig. 35 — Construction of Crocker Wheeler Motor Generator Armature.
A. CARICATURE
W.L!CTOR
RINGS
Fig. 36 — Showing Crocker Wheeler Motor Armature with Coil Terminals Unsoldered.
Alternating current transformers for the production of high voltages may be broadly
classified under two general types :
(1) The constant current transformer;
(2) The constant voltage transformer.
In terms of the ratio of transformation, they may be classified as :
(1) Step-up transformer;
(2) Step-down transformer.
According to the design of the coils and the core or magnetic circuit, they may be
classified as :
(1) Open core transformer;
(2) Closed core transformer;
(3) Auto transformer;
(4) Air core transformer.
Fig. 37 is an elementary diagram of a closed core, step-up, constant voltage transformer.
The primary and secondary windings P and S respectively, are supported by a rectangular
iron core built up of strips of sheet iron. The primary winding, for example, may consist
of one or two layers of comparatively coarse wire such as No. 10 or No. 12 B. & S. gauge.
The secondary winding S may have several thousand turns of fine wire such as No. 30 or
No. 32.
The process of transformation is as follows : The alternating current flowing from a
dynamo through the primary winding P magnetizes the iron core periodically, causing a
ELECTROMAGNETIC INDUCTION.
35
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varying flux to flow through the iron core in accordance with the alternations of current.
This varying flux induces an E. M. F. in the secondary which will cause a current to flow if
the secondary circuit is closed. The current in the secondary circuit flows in the opposite
direction from that in the primary circuit and as it increases, it sets up a flux in opposition
to that already in the core, reducing its strength. This reduces the self-induction of the
primary, permitting more current to flow
in the primary and in this way the
transformer becomes self-regulating —
a rise of the secondary current causing
an increase in the primary current.
If, for example, current at 110
volts, 500 cycles, flows through
winding P, the flux will alternate
through the core 1,000 times per
SeCOnd, Setting Up 1,000 alteriia- Fig. 37-Mnguetie Circuit of Step-up Closed Core
tions of current in winding S. Transformer.
Since S consists of a great number of turns, the voltage of the current induced in
S will be very much greater than the voltage of the current in winding P. In
fact, it is found that the voltage in the secondary winding is almost a direct
ratio of the primary and secondary turns, e. g.,
E-s T-s
E-p ~T-p
where T-p = the current in the primary ;
where T-s = the current in the secondary ;
E-p and E-s = the voltage in the primary and secondary circuits respectively.
Hg. 38 shows the open core, step-up voltage, constant current transformer employed
C, the core constructed of a bundle of fine iron wires or of sheet
iron is covered with several layers of
insulating cloth followed by one or two
layers of coarse copper wire. An insu-
lating tube (not shown) is placed over
the primary. It is made of some mate-
rial which will withstand the heat and
possess the requisite insulating qualities.
Over this tube is placed a secondary
winding which consists of several
thousand turns of fine wire wound up in
the form of pancakes as at S-l, S-2, S-3.
There is little magnetic reaction of the
secondary upon the primary in this type
of transformer owing to the lack of a
continuous iron path for the flux and the
self-induction of the primary therefore
remains nearly constant. The transform-
er will draw practically the same current
when the secondary is on short circuit as when it is open.
The closed core transformer can be designed to have this operating characteristic when
fitted with a magnetic leakage gap shown by the dotted line, Fig. 37. The reactive lines
of force from the secondary pass through this gap and the self-inductance of the primary
winding, therefore, remains nearly constant under all variations of the secondary load.
Both the open and closed core transformers are employed in wireless telegraphy to
generate current at voltages between teii thousand and fifty thousand volts at power input
varying from Y4 K. W. to 500 K. W.
The ratio of transformation in the open core transformer is not exactly in proportion
to the turns, due to magnetic leakage. The design is, therefore, altered to meet these
conditions. Generally the secondary is given more turns than the usual transformer equation
would require.
The so-called auto transformer with a step-up ratio of turns is shown in Fig. 39. In
this type the primary and secondary windings have turns in common, a single coil being
Fig. 38 — Open Core Transformer.
36
PRACTICAL WIRELESS TELEGRAPHY.
39 — Auto Transformer,
copper strips, the tubing being from l/> to
used for both circuits. A portion of the current flowing in the secondary winding is in-
duced by the passing of the flux through the core from the primary turns, but another
portion flows into the secondary circuit by direction conduction.
Although transformers of this type are not employed for the production of high voltages
(with low frequency currents), they are frequently used as step-down transformers to
obtain 10 to 30 volts of alternating cur-
rent from a 110- volt source. Without an
iron core, auto transformers are used in
the circuits of radio frequency in both
the transmitting and receiving apparatus
of wireless telegraphy.
The air core transformer in Fig. 40 is
used principally in radio-frequency cir-
cuits for transferring oscillations at ex-
tremely high frequencies from one circuit
to another, and when used in this man-
ner it might properly be called a radio-
frequency transformer. For such a trans-
former if used in the transmitting ap-
paratus of a radio set, winding P is made
of a few turns of coarse copper tubing or
inch in diameter for the small size sets. Wind-
ing S may have several turns, a dozen or more of insulated wire or small copper tubing.
On the other hand, if the auto transformer is used in receiving sets, winding P may consist
of several hundred turns of No. 24 B. & S. wire, and winding S may have several hundred
turns of No. 32 B. & S. wire.
Whether or not the voltage of the sec-
ondary circuit will be greater or less than in
the primary, in radio-frequency transforma-
tion, depends upon the values of capacity
included in either circuit as well as the ratio
of the turns. Owing to the phenomenon of
resonance and the effects of capacity, a step-
up ratio of turns may be the equivalent of a
step-down voltage or vice versa.
When the primary circuit of an open core
transformer is supplied with interrupted di-
rect current, it is called an induction coil.
This coil will be described in detail in Para-
graph 50.
44. Electrostatic Capacity.— In or-
der that certain phenomena involved in
the flow of alternating current may be
understood, it will be necessary to con-
sider another quality of an electric cir-
30,000 TO
1,000.000
CYCLES
SECONDARY
PRIMARY
Fig. 40 — Radio Frequency Transformer.
cuit known as electrostatic capacity. We have mentioned two qualities of an
electric circuit, i. e., resistance and inductance. The third quality, capacity, is of
particular importance in wire telegraph apparatus and will now be defined.
Further on, we shall show how
c these three qualities govern the flow
of an alternating current.
Capacity may be defined as that
property of a conductor or circuit
by which energy can be stored up in
electrostatic form. The electrostatic
capacity of a conductor is measured
by the quantity of electricity in
coulombs with which it must be
charged to raise its potential to one
volt/
EFFECTIVE VALUE 10 5 AMP
Fig. 41— Rise and Fall of Alternating Current.
ELECTROMAGNETIC INDUCTION.
STATIC FIELD
Fig. 42 — Simple Condenser.
A device for storing up energy in the form of an ^electrostatic field is known as a
condenser. When two copper sheets or other conducting material are separated by a
small air space as in Fig. 42, and a source of direct or alternating current connected to
the two plates, the intervening space fills
up with electrostatic lines of force. If
the charging source be disconnected, and
the terminals of the condenser be recon-
nected to a galvanometer, the latter will
give a momentary deflection indicating
the passage of an electric current. This
experiment proves that the electrostatic
field within a condenser will, when re-
leased, set up a flow of an electric current.
The unit for expressing the ca-
pacity of a condenser is the farad
which is a condenser of such dimen-
sions that one volt of electricity will
store up in it a charge of one
coulomb. The farad is too large for practical measurements, hence the micro-
1
farad is in general use. One (1) microfarad = - farad.
1,000,000
The quantity of electricity that can be placed in a condenser is directly proportional to
its capacity and the difference of potential between its plates, or Q — C X E- Hence, a
condenser of .000002 farad capacity, charged to a potential of 10,000 volts would have
stored up in it 10,000 X .000002 — .02 coulomb.
When current flows into a condenser, its potential difference rises uniformly until the
E. M. E. of the condenser and that of the charging source are equal. At any instant,
Q
the E. M. F. of the condenser is proportional to — but since the charging process is uniform
C
E
the average E. M. F. = — .
2
The work done in joules in placing a quantity of electricity into a condenser — the
quantity of electricity multiplied by the average E. M. F., hence
E
the work in joules = Q X —
2
Since Q = E X C
C E2
therefore W — EXCX — —
2 2
Where W = the work in joules.
Now if a condenser is charged N times per second, the power is expressed:
C E2
P=i- - X N
2
. Where N = the number of charges per second ;
C =i the capacity of the condenser in farads ;
E — the potential difference in volts.
Hence if a condenser of .002 microfarad capacity were charged to a potential of 30,000
volts by a 500 cycle alternator, the power expended in watts would be :
.000000002 X 30,0002
• X 1,000 = 900 watts.
2
A condenser of concentrated capacity always consists of :
(1) Two or more opposing surfaces;
(2) An insulating medium between the plates which may be air or any of the well-
known insulating materials, such as glass, micanite, hard rubber, waxed paper,
etc.
38 PRACTICAL WIRELESS TELEGRAPHY.
This medium is known as the dielectric. The capacity of a condenser is found to vary:
(1) Directly as the area of the opposed surface and the ability of the dielectric to
conduct electrostatic lines pf force;
(2) Inversely as the separation of the plates.
This may he written :
K X A X 2248
T X 1010
Where C = the capacity of the condenser in microfarads ;
A = the area of the opposed surfaces in squares inches ;
K = a certain constant ;
T = the separation of the opposed surfaces, or the thickness of the di-electric.
It can be proven that different di-electric mediums conduct static lines of force
with more or less ease depending upon their nature. Air is taken as unity and
all other insulating mediums are compared to it. Certain grades of glass are
said to have a dielectric constant of 9, meaning that a condenser with a plate of
glass between conducting surfaces will permit 9 times the quantity of electricity
to be stored up as with air at ordinary pressure. In the same way, the dielectric
constant of micanite is said to be 5, paraffin paper 2, etc. (Note complete table in
the Appendix).
Condensers of large capacity are made by taking a number of sheets of tin or brass
foil and separating them with thin sheets of waxed paper or other insulating material,
alternate sheets of foil being connected together on either side, so there is no direct con-
nection between them. This constitutes a condenser of concentrated capacity which may
store up temporarily considerable amounts of energy in electrostatic form.
Condensers may be classified with respect to their dielectric strength which may be
defined as the ability of the dielectric to resist puncture when subjected to electric pressure.
Condensers which will withstand high voltages without rupture of the dielectric are termed
high potential condensers and conversely those which will withstand low voltages only are
called low potential condensers. High voltage condensers are used in circuits of several
thousand volts pressure. Low voltage condensers are employed in circuits of less than
500 volt pressure.
We have mentioned that a condenser when first connected to a charging
source, has zero potential, and as the current flows, the potential difference rises
until the voltage of the condenser is equal to voltage of the charging circuit ; the
flow of current then stops. If the applied potential is decreased, the condenser
will start to discharge and current will flow out in the opposite direction to
which it was charged. The voltage of the condenser is thus seen to set up a
back pressure which tends to drive the charging current back.
We have already seen how inductance tends to prolong the flow of current in
a circuit and we now see that the condenser tends to extinguish it or drive it
back. Thus the back pressure of the condenser opposes that set up by an in-
ductance coil. We shall now see how these counter E. M. F.'s govern the flow of
alternating current.
The effects of self-inductance will first be noted.
45. Reactance and Impedance. — When a coil of wire is connected to a
source of direct and then to a source of alternating current of the same voltage,
the flow of current (in amperes) will be considerably greater with the former
connection than with the latter. This is due to the fact that the counter E. M. F.
of self-induction in a direct current circuit is only momentary, the effects being
observed when the current is turned on and off, whereas in a circuit carrying
alternating current, the effects of self-induction are continuous and the back
pressure resulting therefrom must always be considered to determine the strength
of current.
The flow of a direct current through a given circuit is opposed only by the
ohmic resistance, but the flow of alternating current is impeded by the counter
electromotive force of self-induction as well as by the ordinary resistance. The
ELECTROMAGNETIC INDUCTION.
39
extra resistance of self-induction is termed reactance, and is expressed in equiva-
lent ohms. The combined opposition of reactance and resistance in any circuit is
termed impedance, and accordingly the flow of current through a circuit carrying
alternating current is governed by the impedance and not alone by the ohmic
resistance. It should be understood that the counter E. M. F. of self-induction
entails no loss of energy in an electric circuit as does resistance (where the
energy is lost in the form of heat), but a higher voltage is required in that
circuit to force a given value of current through it.
The flow of alternating current is nearly always controlled by coils of high
self-induction which are termed reactance coils or "choking" coils.
The reactive pressure occasioned by a circuit loaded with inductance is termed in-
ductance reactance. It is expressed :
Reactance = 6.28 X N X L
Where N — the frequency in cycles per second.
L =.the inductance in henries.
If the coil L of Fig. 43 has inductance
of .055 henry, and it is connected to a 60-
cyqje alternator, the inductive reactance
= 6.28 X 60 X -055 = 20 ohms. If the
frequency be increased, the reactance (in
ohms) increases in the direct ratio; thus
if N == 100,000 cycles, the frequency of
a radio-frequency alternator, then the
reactance of coil L = 34,540 ohms.
The flow of current through L is
governed both by the reactance and the
resistance, and the impedance of such a
circuit is expressed as follows :
60 CYCLES
A C
43 — -Alternating Current Circuit with Concentrated
Inductance.
Impedance = V
Where R = the resistance of the coil in ohms;
X = the reactance of the coil in ohms.
Then if the coil L of Fig. 43 had inductance of .055 henry, resistance of 10 ohms and
reactance of 20 ohms, then
Impedance = V 202Xl02 = 22.3 ohms approximately.
E
For direct or continuous current, Ohm's law is expressed I — — , but for alternating
R
E
current the formula is modified to, I =r — . If the pressure of the alternator is 110 volts,
Z
110
then there will flow through L, - - — 4.9 amperes nearly.
22.3
46. Capacity Reactance. — We have shown how a condenser connected in
series with an alternating current circuit acts as an effective resistance and exerts
a back pressure on the charging E. M. F., and also that this back pressure opposes
that set up by inductance. To distinguish these counter E. M.'F/s, the reactance
occasioned by inductance is expressed as positive reactance and that by a con-
denser as negative reactance,
The capacity reactance of a condenser is determined as follows :
1
Capacity reactance = —
6.28 X N X C
Where N = the frequency of the current in cycles per second ;
C = the capacity of the condenser in farads.
The important point to be noted from this formula is that a large condenser will have
a small value of reactance and conversely a small condenser will have a large value of
reactance.
40
PRACTICAL WIRELESS TELEGRAPHY.
If the condenser C connected in series with the 60 cycle alternator of Fig. 44 has capacity
of .00013 farads, and the frequency of the alternator is 60 cycles, then
1
Capacity Reactance = = 20 ohms approximately.
6.28 X 60 X .00013
If the frequency of the alternator is 100,000 cycles, then,
1
Capacity Reactance =
— = .012 ohms.
6.28 X 100,000 X -00013
It is clear that by proper selection of capacity and inductance values in the alternator circuit
of Fig. 45, the counter electromotive forces can be made to balance and the reactance there-
1
fore reduces to zero, or 2ir N, L = —
27T N,C
The circuit then acts as if neither induct-
ance or capacity were present and the
flow of current is governed solely by the
ohmic resistance of the circuit.
If capacity reactance overbalances in-
ductance reactance, then the resultant
value takes the notation of the predom-
inating figure, e. g., if the capacity react-
60 CYCLES
A C
Fig. 44 — Alternating Current Circuit with Condenser
Series.
>" ance exceeds the inductance reactance, the
difference between the two will be ex-
pressed in ohms, and the circuit said to have so many ohms capacity reactance. In case
inductance reactance predominates, the opposite statement applies. We see from all this
that a much greater current can be made to flow through the circuit from the alternator
by the use of a condenser and a coil than if but one of these were used.
Reviewing the foregoing, it is clear that the reactance of a given coil for frequencies
in excess of 100,000 cycles per second (as compared to lower frequencies) may attain a
rather large value. It is therefore nec-
essary in such circuits to insert a cer-
tain amount of concentrated capacity to
build up the current. In the radio-
frequency circuits of wireless telegraph
apparatus, current flows at frequencies
between 20,000 and 1,000,000 cycles per
second and if this current is to be trans-
ferred by magnetic induction from one
circuit to another, the second circuit
must contain a certain amount of in-
ductance and capacity of such values
that inductance reactance and capacity
reactance neutralize one another. The
60 CYCLES
A.C
Fig. 45 — Showing How Resonance Is Obtained in Alter-
nating Current Circuits.
second circuit is then said to be resonant to the impressed frequency and the flow of current is
governed solely by its resistance.
Straight wires possess both capacity and inductance, which are said to be dis-
tributed rather than concentrated as in the case of a condenser or a coil of wire
The laws of electrical resonance apply to such circuits as well as those having
concentrated capacity and inductance.
47. Lag and Lead of Alternating Current. — A certain phenomenon, in-
volved in the flow of alternating current throughout a given circuit, is termed
phase displacement. Given a circuit in which inductance reactance predominates,
it is found that when a given alternating electromotive force is applied thereto, the
pressure and current do not reach their maximum values simultaneously. The
current lags behind the impressed voltage by a certain degree dependent upon the
self-induction of the circuit and such a circuit is said to haye a lagging phase.
As it is convenient to express a complete cycle of current in terms of the degrees of a
circle, l/4 cycle being equivalent to 90°, l/i cycle to 180°, and so on, we express the lag of
the current in terms of the degrees of the circle. Hence, a certain circuit is said to have
ELECTROMAGNETIC INDUCTION. 41
an angle of lag of 35° or some other degree dependent upon the constants of the circuit.
(All this is explained in any strictly theoretical text book on alternating current).
In a circuit wherein capacity reactance predominates, the opposite condition is obtained,
e. g., the current leads the voltage reaching its maximuhi value before the impressed
E. M. F. A circuit of this type is said to have a leading phase.
The point to be brought out here is that in circuits having either lead or lag, the actual
power consumption in watts cannot be determined from the reading of a voltmeter or
ammeter. To illustrate : When a voltmeter or ammeter are connected in the primary wind-
ing of a high voltage transformer of the type used in wireless telegraph transmitters, the
voltmeter may indicate 110 volts and the ammeter current strength of 14 amperes. Apply-
ing the power formula in simple form the apparent reading in watts would be 110 X 14 =
1,540 watts, but a wattmeter connected in this circuit may indicate a reading of 1,000 watts
which is the true reading because the wattmeter is constructed to read correctly inde-
pendently of the degree of phase displacement. The result obtained by multiplying the
pressure by the current is only an apparent reading of watts ; but the true reading is
always obtained by the meter. The ratio of the true watts to the apparent watts is ex-
pressed by the term, the power factor. Tn the circuit taken as an example, the power
1000
factor = — , or approximately 65%.
1540
R
The power factor can also be obtained from the ratio of — , that is if the impedance
Z
and resistance are known, and the value of the former is divided by the latter, the power
factor of the circuit is obtained.
lie formula for power in direct current circuits, W = I X E is changed in the case
of an alternating current circuit wherein the current lag's behind the voltage to read :
W i= I X E X Cos. 0.
The cosine <i> is the power factor expressed as a function of an angle of a circle and
R
as mentioned, is equal to — . Hence if the total resistance of a given circuit is known, also
Z
the total impedance and the reading of current and E. M. F. is obtained by an ammeter and
voltmeter respectively, we can determine the true power in watts in any circuit without the
use of a wattmeter.
48. Effective Value of Alternating E. M. F. and Current.— It is self-
evident from the alternating current curve of Fig. 41 that the current constantly changes
in value' as well as reversing its direction. Hence, to express the effectiveness of a given
electromotive force in such circuits, we must employ some value other than the maximum
E. M. F. or maximum current per alternation. Take, for example, any given circuit in
which the maximum current for each alternation amounts to 15 amperes (as in Fig. 41),
it is evident that at all points off maximum during the complete cycle, the strength of the
current is less than 15 amperes. It is clear that we must take some sort of an average
value in order to determine the effectiveness of an alternating current. Since the heating
effects of direct current in a given circuit are uniform, the effectiveness of an alternating cur-
rent is expressed in terms of the strength of a given amount of direct current which would
produce the same power or heating effect. To illustrate: If 15 amperes of direct current
pass through a resistance of 2 ohms, the power of the current converted to heat will be
\- X R = 152 X 2 = 450 watts. Now if we pass an alternating current through the
same wire and adjust its strength until 450 watts are consumed in the form of heat,
we would then have 15 amperes of alternating current flowing.
This is the so-called effective value of the alternating current which in the case of
a sine wave curve is found to be .707 of the maximum value per alternation. Suppose,
the maximum value of current per alternation in the curve of Fig. 41 is 15 amperes,
then the effective value will be 15 X -707 •=. 10.5 amperes. That is, the current rises
and falls uniformly between a value of -(-15 amperes and — 15 amperes producing the
same heating effect as a direct current of 10.5 amperes. Now an ammeter connected
in such a circuit would indicate 10.5 amperes because these instruments are constructed
to indicate the effective value of current and not the maximum value per alternation.
Similarly, voltmeters indicate the effective voltage in a given circuit. All this means
that the maximum voltage per cycle of an alternating current supplied from power mains at
42
PRACTICAL WIRELESS TELEGRAPHY.
pressure of 500 volts, is somewhat greater, in fact, is 500 X 1.41 = 705 volts. Similarly the
maximum voltage per alternation in 110 volt alternating current circuits is 155 volts. (This
is only true when the wave form of the current follows the curve of sines.)
When speaking of the pressure of the high voltage transformers used in wireless
telegraphy, the secondary voltage is generally given as the maximum voltage per
cycle and not the effective value.
The student will see from the foregoing that the problems of alternating current
circuits are largely different than those of direct current circuits and that the flow of
current is governed by conditions other than the ohmic resistance. Also the actual
power consumption in watts depends upon whether or not the pressure and current in a
given circuit are in exact phase.
49. Measuring Instruments or Electric Meters. — The principle measuring
instruments employed in connection with a wireless telegraph transmitter are :
(1) The voltmeter;
(2) The ammeter;
(3) The wattmeter;
(4) The frequency meter;
(5) The hot wire ammeter.
In the circuits of a radio-transmitter, these instruments occupy the positions fol-
lowing: The voltmeter is joined across the terminals of the alternator; the ammeter
is connected in series with the primary winding of the transformer; the wattmeter is
connected in the circuit from the alternator to the transformer; the frequency meter
is shunted across the terminals of the alternator; the hot wire ammeter is used prin-
cipally in circuits of radio-frequency, and to some extent, in circuits of lower frequency.
Before entering into a description of these meters, we shall explain the workings
of the current-detecting instrument knovi
the galvanometer. This instrument may
take one of several forms, but the type
shown in Fig. 46 is the least difficult to
understand. A rectangular coil of sev-
eral turns of copper wire D is suspended
between the poles of a horse shoe
permanent magnet, P, P. Between the
poles is the stationary iron core C* The
coil is suspended from the screw F and the
current to be measured enters at the wire
A and leaves by the wire B. When
current is passed through the coil B, it
tends to turn so as to include the greatest
number of lines of force but is resisted by
the torsion of the suspending wires. If a
pointer and suitable scale are attached to
this coil, comparative readings of the
strength of current may be made. In-
struments of this construction are sen-
sitive and will easily measure a current
of .000001 of an ampere. It is an impor-
tant instrument to demonstrate the ele-
mentary principles of electromagnetic
induction, and should be a part of all
students' equipment.
Now if the coil D had several
Fig. 46 — Simple Galvanometer.
thousand ohms resistance, the galvanometer might be calibrated in volts and em-
ployed as a voltmeter. If, on the other hand, coil D were wound with a few turns
of relatively coarse wire, it might be calibrated in amperes and would, therefore,
be known as an ammeter. As an ammeter it would be connected in series with the
circuit under measurement.
*The Core C intensifies the field across the air gap P to P.
ELECTROMAGNETIC INDUCTION.
— vWW
(a) The voltmeter may be constructed along the lines of galvanometer. A
simple drawing of the Weston voltmeter appears in Fig. 47.
A rectangular coil of fine wire, A, B,
is mounted on the metal bobbin G. It is
supported by jewelled bearings and held
in the zero position of the scale by the
spiral springs, S-l and S-2, through
which the circuit of the coil is com-
pleted. When the pointer is in zero po-
sition, the coil rests at a slight angle to
the pole pieces of a permanent magnet.
N, S. When current is flowing through
the coil, the normal field from N to S is
"lengthened" out and in trying to "shorten"
themselves, the lines of force actually
"twist" or turn the coil. When the tension
of the spring is equal to the pull of the
magnetic field, the pointer comes to rest
and the reading of the instrument may then
he observed. An external resistance coil,
R, is connected in series with the winding
of the bobbin to reduce the flow of cur-
rent to a minimum value. This coil may
have resistance of 100,000 ohms and may
be provided with two taps making the
meter a double scale instrument.
There is essentially no difference in
the construction of the ammeter and
the voltmeter except the resistance of the windings and the calibration. The coils
of the ammeter have relatively low resistance whereas the voltmeter as already
mentioned, has high resistance.
The windings of an ammeter may be proportioned to carry a small amount of current,
but the meter can be used to measure very large values by connecting its terminals
across an external shunt as in Fig. 48.
This shunt consists of a number of metal
strips of comparatively low resistance
stretched between two large copper
lugs. A potential difference exists across
the terminals of the shunt which causes
a certain amount of the current to sub-
divide and flow through the meter. An
increase of current through the shunt
will increase the flow of current through
the instrument, and the meter, therefore,
may be calibrated to read very large Flg" 48-Show'«* the Use of a Shunt Wlth an Ammeter"
values of current, although but small values pass through the instrument itself. Such
instruments are generally supplied with a certain length of connecting leads between
the shunt and the instrument. The length of these leads must not be altered or the
calibration of the instrument will be interfered with. In electrical diagrams, both the
voltmeter and the ammeter may be designated by the symbol of Fig. 49.
One type of meter for use in alternating current circuits is shown in Fig. 50. Coil
VV is a spool of wire with several layers like the winding of an electromagnet. The
shaft carrying the pointer P has the semi-cylinder of iron A surrounded by the brass
semi-cylinder B. Outside B is another semi-cylinder of iron C. When current is flow-
ing through the coil W, the semi-cylinder A tends to move into the unfilled space of
C, but is resisted by the spiral springs S.
If coil W is wound with fine wire and has a coil of high resistance connected in series,
it is a voltmeter, but if W has a coarse wire winding, the instrument becomes an ammeter.
(b) The wattmeter is a positive necessity for determining the power flowing
AMMETER
LOAD
44
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 49— Symbol for Measuring Instru-
ment.
in an alternating current circuit because, as already explained, the product of the
volts multiplied by the amperes does not give the true reading of watts. Due to
the self-induction of the circuit, the E. M. F. and current do not reach their maxi-
mum values simultaneously. The current in fact,
lags behind the impressed E. M. F., and there-
fore the product of volts multiplied by amperes
gives what is known as an apparent reading of
watts. This lagging of the current behind the
E. M. F. is known as phase displacement.
Wattmeters are constructed to be independent
of phase displacement and they will give true
readings of power consumption over the range
for which they are designed. The student will
always recognize the wattmeter by it having four
binding posts; tzvo very large binding posts which
are connected in series with the apparatus under
measurement and two small binding posts which
are connected in shunt to the terminals of this
apparatus.
The general design for this instrument is shown in
Fig. 51. Coil A, called the current coil, is connected
in series with the load; coil B, called the voltage coil, is connected in sliunt to the load
but a large resistance R is connected in series. The position of the coil A is fixed, but
coil B is mounted on bearings and fitted with a pointer P which is held in the zero
position by a spiral spring S. When current is passed through these two coils, two
magnetic fields are set up, which act mutually to pull the movable coil B parallel to the coil A.
The current in the pressure coil will vary as the potential difference between its
terminals and the current through the series coil will vary as the current in the circuit
in which it is inserted. The force acting
upon the movable coil will be proportional
to the product of the current and potential
difference. That is, the deflection of the
coil is proportional to the power of the
current flowing in the circuit, and the
scale of the instrument may be calibrated
directly in watts. In the diagram binding
posts C, C, are for the current coil, and
posts V, V, are for the pressure coil.
(c) Frequency meters are not ex-
tensively supplied to commercial wire-
less telegraph sets, but one of these in-
struments is always a- part of the radio
inspector's testing equipment. The
Hartmann & Braun meter is shown in
Fig. 52. It has much the appearance Fig-
of a voltmeter, and, like that instrument, it is connected in shunt to the terminals
of the alternator.
In this diagram the single elongated magnet winding M has joined in series with
it the coil R ; the two terminals E, E are shunted across the circuit under measurement.
The soft iron piece, P, P, completes the magnetic circuit for the poles of the horse-
shoe magnet, N, S, N, S, etc. A number of small vibrating reeds are placed directly
in the path of the flux between the soft iron piece and the poles of the magnet. Each
of these reeds have a different period of mechanical vibration and, consequently, are
only set into vibration by the flux of the magnet when it alternates at such rates as to
correspond to the natural mechanical period of the reed.
Four permanent horse-shoe magnets, N, S, N, S, etc., keep the core in a constant
ELECTROMAGNETIC INDUCTION.
45
LOAD
state of magnetization, but wh'en alternating current flows through winding M, the
reed having a natural period corresponding to the particular frequency of the current
flowing will be set into violent oscillation. The scale reading corresponding to this
particular reed is the frequency of the cir-
cuit under measurement. The instrument
will perhaps be better understood from
the side elevation, Fig. 52. Frequency
meters of this type are very accurate.
(d) The mechanism of one typt
of hot wire ammeter is shown in Fig.
53. Meters of this construction are
particularly suitable for measurement
of the current at radio-frequencies. It
should be self-evident that measure-
ment instruments having bobbins or
coils of wires are totally unsuited to
this work, first, because the current
of high voltage and high frequency
would burn out the coil, and, second,
the length of the windings would
seriously affect the oscillating prop-
erties of the circuit. The self-induc-
, • ^ 5 ' *c ^> tion of the hot wire in a hot wire
l/n p meter is practically zero, and there-
fore there is no danger of burn-out
or short circuit.
In the diagram, Fig. 53, a steel plate
P is made to pull against the wire C, D,
by the spring S-l. One end of the wire
C, D is attached to the plate P, passed
about the pulley K, and again attached to P at point R where it is insulated. The pulley K
carries the arm S with two prongs between which is stretched a silk thread T wound
around the shaft X. X carries the pointer P1, which moves over the scale.
The current to be measured enters the wire at point A and leaves at the shaft K;
as the current flows, the temperature of the wire rises, causing it to expand, but owing
to the tension of S-l, the slack is taken
up at side B and equilibrium can be re-
stored only when the pulley K rotates
sufficiently to equalize the pull on the
spring. The rotation of K carries S
with it, and S in moving causes the silk
fiber to rotate the shaft which carries
the indicating needle.
When the hot wire ammeter is used
to measure large values of current, a
shunt must be supplied to sub-divide the
current flow, but an inductive shunt,
even jvith one-half a turn of wire can-
not be employed to measure current at
radio-frequencies because the inductance
of the shunt would vary with each
change of frequency. Consequently, hot
wire meters are constructed after the de-
Fig. 51 — Mechanism of Wattmeter.
sign of Fig. 54, where several resistance
Fig. 52 — Mechanism of Frequency Meter.
wires are stretched in parallel between two large copper blocks, B, B1. All of these
wires are of small diameter, such as No. 36 or No. 40 B. & S. gauge, hence they offer
practically the same resistance to current of radio-frequency as to a direct current;
that is, irrespective of the frequency of the current, the reading in amperes will be
accurate. One of the wires, C, D, is selected to work the indicating mechanism in the
46
PRACTICAL WIRELESS TELEGRAPHY.
DAMPING
DISC
Fig. 53 — Mechanism of Hot Wire Ammeter.
following manner: A wire, E, F, is attached to the center of C, D, and a silk thread
attached to it at K, which is wound about the shaft in such a way as to work against
the tension of the spring S which, normally, would cause the pointer to move to the
full scale position. However, by means of the thread, it is drawn to the zero position
of the scale. When current is flowing through C, D, the expansion of the wire releases
the pull of the thread which allows the
pointer to move across the scale ac-
cording to the degree of expansion and
the tension of the spring.
The fundamental principle of another
instrument for measuring radio-frequency
currents, used by the Marconi Company,
is shown in Fig. 55. The complete details
for construction are not opened for pub-
lication, but briefly, the operation is as
follows : The current of radio-frequency
Hows through several wires stretched be-
tween blocks B and B1. A thermo-
couple mounted on one of these wires
as indicated at C, D, is heated by the
current of radio-frequency flowing be-
tween the copper blocks. As is well
known, this junction sets up a direct
current which flows through the
meter A. The latter is a sensitive di-
rect current 'instrument with magnetic
windings, and is calibrated directly in
amperes.
The production of E. M. F. by a thermo-couple may be better understood from Fig.
56. If a piece of bismuth B and antimony A be soldered or welded together and
their ends connected to a galvanometer, then if the temperature of the junction is
raised higher than the remainder of this circuit, a current flows in the external circuit
from antimony to bismuth. If the junction is cooled below temperature of the rest
of the circuit, current will flow in the opposite direction. There are a number of
other metals which when joined and heated will produce a direct E. M. F. under
change of temperature, notably copper and iron, which are frequently used as a thermo-
junction.
50. Induction Coil. — \Ye have shown how an alternating current can be
raised to a pressure of several
thousand volts by means of the alter-
nating current transformer. In a
somewhat .similar manner,, a direct
current of low voltage can be changed
to an alternating current of many
thousand volts by an apparatus
known as an induction coil.
Fig. 57 is a diagrammatic sketch of
an induction coil. P is the primary
winding and S the secondary winding.
B is a piece of spring brass fitted with
a soft iron button that may be attracted
by the core C. A is an adjustable thumb
screw, platinum tipped, which makes
contact at C1, closing the circuit of the battery through winding P. In practice sole-
noid S is wound about C.
When the battery circuit is closed at K, the core becomes saturated with magnetism
and attracts the armature B. B being drawn to the end of the iron core, the flow of
current is broken at C1. Since the current is now cut off from P the magnetic field
disappears and the tension of the spring causes the circuit to be closed again at C1.
This process is repeated continuously, resulting in from 30 to 100 breaks per second.
Hot Wire Ammeter with Internal Shunt.
ELECTROMAGNETIC INDUCTION.
47
9
The coil P generally has 1 or 2 layers of coarse insulated copper wire of different
sizes (according to design) between No. 12 and No. 16, which are thoroughly insulated from
the core C. Winding P is covered with an UILLIAMMFTFR
insulating tube which supports winding S.
The secondary winding may have many JUNCTION
thousand turns of very fine wire which
are wound in the form of pancakes and
connected in series. Thus the electromo-
tive force at the terminals of winding S
Fig. 56 — Production of Thermo-Electric Current.
may be as great as 150,000 volts when
the pressure of the current through P is
20 to 30 volts.
The student should note that, al-
though the interrupted direct current in
winding P induces an alternating current
in the winding S, the induced pressure
(in winding S) is considerably more in-
tense at the "break" of the primary cur-
rent than at the "make." This is due
to the more rapid change of flux thread-
ing through the winding S when the lines
of force collapse than when they rise; in
Fig. 55-Aerial Ammeter with Thermo-Couple. othef WQrds? it requires a longer period
to saturate the iron core with lines of force than to empty it. The wave form of the induced
current is shown in Fig. 58.
MAGNETIC
AMMETER
B-i
MINI
pig< 57 — Fundamental Diagram of Induction Coil.
48
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 58 — Wave Form of Secondary Induced Currents.
(a) Interrupters. In addition to the magnetic interrupter shown in Fig. 59
there are several types of interrupters for induction coils, but since they are seldom
used in modern wireless systems, they will not be described. The electrolytic
interrupter is frequently employed
but not extensively. A diagram of
connections and a sketch is shown
in Fig. 59.
A lead plate of convenient size is
immersed in a dilute solution of sul-
phuric acid together with a platinum
electrode covered with a porcelain
sleeve. The amount of platinum ex-
posed to the action of the acid is closely
regulated according to the conditions
of the circuit. When the interrupter is
connected in series with the primary winding of the induction coil the action is as follows :
The current flowing through the solution from platinum point to the lead plate sets up an
electrochemical action which form a gas bubble on the tip of the platinum electrode. This
gas bubble insulates the platinum exposed, thereby opening the primary 'circuit. The cur-
rent flow having discontinued, there is nothing to sustain the gas bubble, which accordingly
collapses again, allowing the current to flow through the winding, when the above action
is repeated. A rather high rate of in-
terruption is thus secured which in-
duces a rapidly pulsating current in
the secondary winding. Interrupters of
this type frequently give 1,000 breaks
of the primary current per second of
time. They will not function well on
potentials less than 80 volts direct cur-
rent. Fair results are obtained with
alternating current.
51. Practical Electric Circuits.
— With' the sole purpose of conveying
to elementary students an idea of the
wiring and certain fundamental facts
surrounding practical electrical circuits,
a few examples are herewith appended.
In the circuit of Fig. 60, direct current
at pressure of 110 volts enters at the
terminals A, B, flows through the
fuses F, F, through the switch blades
D, D, and thence on to the bank of
lamps assumed to consist of 8 lamps
connected in parallel or in shunt to the
terminals of the power line. If the
lamps have resistance each of 220 ohms,
one-half ampere will pass through the
individual lamps; hence, 8 lamps will
pass 4 amperes.
Now the voltage of this circuit may
be measured by the voltmeter V which
is an instrument of high resistance,
taking a very small amount of current,
and the current can be measured by the
ammeter A which conversely is an instrument of low resistance. In the problem cited,
ammeter A should indicate current of 4 amperes, and meter V pressure of 110 volts. The
power in watts = 4 X HO = 440 watts = 0.44 K. W.
(a) Fuses. Fuses are required at points F, F, to protect the generator connected to
terminals A, B, from accidental short circuit or overload. These consist of lead or com-
position alloy wire which melts when more than a predetermined number of amperes pass
through them. In order to protect the circuit of Fig. 60, the fuses should have currem
o o o o o
o o o o o
r£j O O O O O
;3 O O O O O
o o o o o
110 V. D.C LEAD' PLAflNUM
Fig. 59 — Electrolytic Interrupter Connected to an
Induction Coil.
ELECTROMAGNETIC INDUCTION.
49
\
LAMPS
carrying capacity of 5 or 6 amperes. Then if current in excess of this value is drawn, the
alloy wire melts, completely cutting off the current.
In the power circuits of the Marconi wireless system, enclosed fuses are employed ex-
clusively. These consist of a strip of fusible material of the requisite current capacity,
stretched between two brass lugs and en-
closed within a fiber cylinder.
A second example of a practical circuit
is shown in Fig. 61 where the terminals
A, B, connect to a 500 volt direct current
generator. Assume that only 110- volt
incandescent lamps were available for light-
ing purposes; then to prevent the lamps
being burned out by excessive voltage they
are connected in series. The complete cir-
cuit will pass y?, ampere of current at a
IF JF pressure of 110 volts. A voltmeter con-
I I nected around any of the lamps would in-
I I dicate approximately 110 volts. Should any
of the lamps burn out, the circuit will be
Fig 60 — Simple Power Circuit. . . , i u i i_i« i_ j i_
broken and can only be established when a
new lamp is substituted for the burnt one. Since the potential across the entire bank of
lamps is 500 volts, and the current ^2 ampere, the bank of lamps would require l/2 X 500 = 250
watts or t/4 K. W.
A third example of a practical circuit is shown in Fig. 62 wherein alternating current
is transmitted, let us say, from a central power station at 2200 volts pressure, passed
through the primary winding of the trans-
former P which is of relatively high re-
sistance. By electromagnetic induction, a
current is induced in the secondary wind-
ing at a pressure of 110 volts with a corre-
sponding increase of current as compared
with that flowing in the primary winding.
This current may be employed convenient-
ly for lighting a bank of lamps such as
indicated at L.
Assume the bank of lamps in this draw-
ing to consist of 8 lamps connected in
rig. 61 — Lamps in Series on 500 Volt Circuits.
parallel; they will require 4 amperes of
current and the fuses at F-l should have
capacity of 5 or 6 amperes. On the other hand, the strength of the current in the primary
winding P is relatively low and much smaller fuses will be employed to protect this circuit.
When electrical energy is transferred from the primary winding to the secondary wind-
ing, certain losses due to resistance, heating of the core and magjietic leakage take
place, hence, the total power flowing through P exceeds that taken from S. If winding S
F
-o~~ o
ZZOO VOLTS
A.C.
Fig. 62 — Showing Use of Step-Down Transformer.
and the circuits associated therewith take 440 watts we may assume a value of 500 watts
for the circuit P. Since the number of watts in a given circuit = I X E, then (assuming
W 500
no phase displacement) I = — or for winding P, I = = 0.22 amperes, the approxi-
E 2200
mate value of the current flowing through winding P. A 1 ampere fuse would therefore
protect the primary circuit from overload.
50
PRACTICAL WIRELESS TELEGRAPHY.
The installation of all types of a power or radio equipment are made in accordance with
certain definite rules or regulations which have been adopted by the National Association
of Electrical Inspectors. These rules vary slightly in different cities of the United States,
but are generally in accordance with the national code. The installation of power or
wireless apparatus should not be undertaken until these rules have been carefully gone over.
The foregoing explanations and examples explain but partially the problems of ordinary
electric circuits, but they serve to show certain fundamental facts which should be of some
value to the elementary student of radio-telegraphy.
Fig. 62a.— A High Power Radio Station in the Tropics.
PART IV.
MOTOR GENERATORS.
HAND AND AUTOMATIC MOTOR STARTERS.
52. THE MOTOR GENERATOR. 53. FIELD RHEOSTATS. 54.
DYNAMOTOR AND ROTARY CONVERTER. 55. THE MOTOR
STARTER. 56. AUTOMATIC MOTOR STARTERS. 57. PROTECTIVE
CONDENSERS. 58. CARE OF THE MOTOR GENERATOR. 59.
How TO REMOVE MOTOR GENERATOR ARMATURE.
52. The Motor Generator. — The required high voltage current for the
operation of a radio-transmitter is obtained from ( 1 ) a source of alternating cur*
rent, (2) an alternating current step-up transformer; but practically all vessels
that have been fitted with radio sets to date have a direct current dynamo making
it necessary to install a motor generator to obtain an A. C. source of supply.
A motor generator is simply a motor and a dynamo coupled together on a com-
mon cast iron base, the motor being set into rotation by direct current, the dynamo
in turn generating an alternating current of the required voltage and frequency.
Such machines may have two or four bearings, two for the motor armature and
two for the generator armature or the shaft may be strengthened at the center and
have both armatures mounted on it. In this case the shaft has two bearings.
MOTOR FIELD
MOTOR /
GEN FIELD
A.C.
Fig. 63 — General Construction of Motor Generator.
A general outline of the construction of a motor generator is shown in Fig. 63 where a
direct current motor is mounted on the left of the cast iron base, the alternating current
generator on the right. The motor receives direct current at pressure of 110 volts (gen-
erally) and the dynamo generates alternating current at frequencies from 60 to 500 cycles
and at voltages varying from 110 to 500 volts according to the design. The student
should note from Fig. 63 that (1) the generator field windings receive current from the
same source as the motor, e. g., in the case of a ship installation, from the ship's dynamo ;
(2) both the motor and generator field windings are connected across the D. C. power line.
52
PRACTICAL WIRELESS TELEGRAPHY.
For the operation of radio-transmitters, a motor generator is required that will give :
(1) Constant speed under variable load;
(2) Constant alternating current voltage under variable load.
For the quenched spark transmitter, a constant current generator having a falling voltage
characteristic under a load is preferred.
When a motor generator is connected to a wireless transmitter, it is subjected
to an intermittent load following the closing of the transmitting key, and there-
MofcrFJe/d
Generator F/'e/c/
Mofor/fteo,
6O-5OO
Cyc/es
Fig. 64 — Simple Shunt Wound Motor Generator.
fore, some means must be provided whereby either a uniform alternating current
frequency or voltage for both can be maintained. In practice the necessary regu-
lation is obtained by special motor field and generator field windings. Hence,
motor generators may be classified with respect to their windings.
Three different types are in commercial use :
(1) A shunt wound motor coupled to a simple alternating current generator:
(2) A shunt wound motor coupled to an alternating current generator, having a
compound wound field:
(3) A motor with differentially compounded fields coupled to a simple alternating
current generator.
An example of type (1) is the 2 K. W. 500 cycle Crocker Wheeler motor
generator used with the Marconi panel transmitters ; of type (2) the 1 K. W. 60
MOTOR GENERATORS.
53
cycle Robbins & Meyers motor generator; of type (3) the 2 K. W. 240 cycle
motor generator. All three types are in use in the radio sets of the American
Marconi Company.
The fundamental circuit of type (1) is shown in Fig. 64; of type (2) in Fig.
65 and of type (3) in Fig. 66. The student should take careful note of the position
of the generator and motor rheostats in all three diagrams because in addition to
Gen l?heo.
60-5OO
Cycles
Fig. 65 — Motor Generator with Compound Generator Field Winding
the automatic regulation which these machines are designed to give, initial adjust-
ments of either voltage or frequency can be made by the rheostats. For example,
if resistance be added at the motor field rheostat, the motor speeds up and, there-
fore, increases the frequency of the generator. If resistance be added at the gen-
erator rheostat, the generator field current reduces and the voltage across the arma-
ture terminals drops. If more current is admitted to the field coils, the voltage of
the armature increases.
Explanations given in Part III will cover the shunt wound motor generator of
Fig. 64. By proper design, fair regulation of frequency and voltage is secured
with this type under the conditions imposed by a wireless transmitter.
54
PRACTICAL WIRELESS TELEGRAPHY.
It will be noted from the diagram of Fig. 65, the generator has two field windings, a
series winding connected in series with the motor armature and a shunt winding connected
directly across the D. C. line. The windings are disposed on each field pole of the gen-
erator so that the lines of force generated by the scries winding and those of the shunt
winding Hozv in the same general direction. When a motor generator of this type is subjected
to load, there will be a tendency towards a decrease in speed, but there will then be an in-
crease of current through the series winding (because it is connected in series with the
O.C
Fig. 66 — Circuits of Motor Generator with Differential Motor Field Winding.
armature) which has the effect of increasing the strength of the generator field, thereby
maintaining the voltage of the alternator fairly constant under variable load. The motor
of this machine has a simple shunt winding with a speed regulating rheostat, connected in
series. The voltage of the generator may be increased or decreased by means of the
generator field rheostat.
The differential motor of Fig. 66 has been explained in Paragraph 40. The principal
advantage of the motor generator in Fig. 66 is that it maintains a uniform speed under
variable load which results in a uniform frequency of current at the terminals of the
alternator.
A photograph of the 2 K. W. 500 cycle Crocker Wheeler motor generator ap-
pears in Fig. 67a wherein the motor generator armatures are clearly shown. The
MOTOR GENERATORS.
55
MOTOR
FIELD
GENERATOR FIELD
Fig. 67a— Details of Crocker Wheeler 2 K. W. 500 Cycle Motor Generator.
generator has 30 field poles and the motor 2 field poles. The armature revolves at
2,000 R. P. M., hence there are 33 1-3 revolutions per second which multiplied
by 30 (the number of field poles) gives 1,000 alternations of current per second.
And since two alternations of current constitute a cycle, the frequency of this
generator is 500 cycles per second. The motor of this machine takes 29 amperes
at pressure of 110 volts D. C, but the generator armature delivers alternating
Fig. 67b — 2 K. W. Crocker-Wheeler Motor Generator Assembled.
56
PRACTICAL WIRELESS TELEGRAPHY.
ROTOR OF
GENERATOR
GENERATOR
- ARMATURE
MOTOR
ARMATURE
Fig. 67c— Details of % K. W. 500 Cycle Crocker Wheeler Motor Generator.
current at pressures varying between 120 and 380 volts with current output of 20.8
amperes. At normal saturation the generator and the motor fields require about
29 X HO
2l/2 amperes each. The complete motor, therefore, is rated at = 4.2
746
horsepower.
Fig. 67a shows the gen-
erator and motor field wind-
ings, the end plates and the
oil gauge of the 2 K. W. 500
cycle motor generator. The
machine completely assem-
bled but with the rotary
disc discharger removed is;
shown in Fig. 67b.
Details of the y2 K. W..
500 cycle Crocker Wheeler
motor generator are shown!
in Fig. 67c and the assem-
bled machine in Fig. 67d.
It is to be noted that the
rotor of the generator is
composed of two toothed'
discs without windings and
Fig. 67d—y2 K. W. Motor Generator Assembled.
MOTOR GENERATORS.
57
that both the field and armature windings are stationary. The rotor closes and
opens the magnetic circuit between the armature and field windings and thereby
induces current in the armature.
53. Field Rheostats.— A type of field rheostat supplied with motor gen-
erators is shown in Fig. 68. A coil of composition resistance wire baked in a
heatproof insulating cement is
mounted in a metal case. The
wire is tapped at intervals and con-
nected to brass studs over which a
sliding contact arm moves. An-
other type used by the Marconi
Company has a number of turns of
bare resistance wire wound on a
slate base. A sliding contact mov-
ing over the turns permits very
close regulation of the flow of cur-
rent in the field winding. A rheo-
stat of this type is essential for
motor generators used with
quenched spark transmitters which
require extremely close regulation
of the generator voltage.
54. Dynamotor and Rotary
Converter. — The dynamotor and
the rotary converter are employed
occasionally to generate alternat-
ing current from a D. C. source of
supply. The distinguishing feature of these machines is the use of a single arma-
ture for both A. C. and D. C., hence, but two bearings are required and the con-
struction of the machine as a whole is simplified. These machines also require
less space to erect, but they possess the marked disadvantage of not allowing
full control over the voltage. Also they are not as efficient as the motor
generator when connected to a radio transmitter.
Fig. 68 — Cutler Hammer Type Field Rheostat.
110 VOLT D.C
A/WW
Fig. 69 — Fundamental Circuit of Rotary Converter.
The rotary converter shown in Fig. 69 has a single winding on one armature
for both alternating and direct current, but the dynamotor of Fig. 70 has two
distinct windings (on the same armature) one to rotate it as a motor and the
other for the production of alternating current.
Explanation of the circuits of the rotary converter of Fig. 69 follows : Direct current
from an external source enters the armature coil C, D through brushes A, B, and also
flows to the shunt field windings (wiring not shown) causing the armature to revolve in
the usual way. Taps taken from this winding at the commutator segments directly under-
58
PRACTICAL WIRELESS TELEGRAPHY.
neath the brushes are connected to the collector rings on the opposite ends of the shaft,
the circuit continuing through the A. C. external circuit E. The voltage of the alternating
current will be maximum when the taps to the collector rings are underneath the brushes
and minimum when midway between the brushes. It is easily seen that as C, D revolves
and attains the position opposite to that in Fig. 69, the current taken from the collector
1 10 VOLT D.C
WWV
Fig. 70 — Fundamental Circuit of Dynamotor.
rings will flow in the opposite direction and therefore as the armature revolves an alter-
nating current can be taken from the armature, the frequency of which varies with
the speed. An important point in connection with this machine is that if the D. C. supply
is 110 volts, the A. C. voltage cannot exceed 70.7 volts. If 110 volts is desired a small
step-up transformer must be used.
The A. C. voltage of the converter may be increased by increasing the speed of the
motor, but the frequency of the current is likewise increased. The converter does not
permit the nicety of control of the voltage and the frequency as does the motor generator
and, therefore, it operates at a disadvantage.
The circuit of the dynamotor is shown in Fig. 70. Here the armature coils for the
production of alternating current have no connection with the coils for direct current.
The two windings are mounted on the same core but in separate slots. The A. C. winding
can be given the correct number of turns so that 110 volts A. C. may be obtained when
the armature is connected to 110 volts D. C.
F-i
00000
no VOLT D.C
Fig. 71 — Cutler Hammer Starting Box Connected to a Simple Shunt Wound Motor.
A small number of either of the foregoing types of machines are in use by the Marconi
Wireless Telegraph Company of America but the rotary converter is very popular abroad.
55. The Motor Starter. — It has been mentioned in Paragraph 40 that
the counter E. M. F. of a motor armature is very low upon starting, and if the
terminals of a motor were connected directly to the source of current, an exces-
sive current would flow which might injure the commutator or burn out the
armature windings (unless the circuit is properly fused). A motor starter is,
therefore, required to reduce the starting current to a safe value.
A diagram of the Cutler Hammer hand starter is shown in Fig. 71. The principal
MOTOR GENERATORS.
59
elements of the starter are the resistance coils R-l, the small holding magnet M and the
handle H. The coils of R-l are of German silver wire or composition wire tapped at
certain intervals and connected to the studs 1, 2, 3, 4, 5. The circuit from the negative
side of the D. C. power line may be traced to the L post of the starter through the handle
H which when placed on the first point of contact permits the current to flow through the
coils of R-l to the terminal A, thence to the brush F of the motor armature. The circuit
continues through the armature coils back to brush E and to the positive side of the line.
One terminal of the field windings
F-l and F-2 receives current at the
positive side of the line at brush E,
but the other terminal has the field
rheostat R-2 connected in series,
also the holding magnet M ; also this
circuit continues to the first tap on
the resistance coils R-l. Now as
the handle is moved slowly across
the contact studs on the starter
current is admitted to the motor arm-
ature by small increments which sets
it into rotation, the speed gradually
increasing as the handle moves
toward the final or full running po-
sition. When this position is at-
tained, the magnet M grips the
handle and holds it in position until
it is released by opening the main
D. C. line switch. The diagram
shows the Cutler-Hammer starter
connected to a shunt wound motor.
It is important that a motor
be started neither too rapidly nor
too slowly. If the former condi-
tion obtains the fuses in series
Fig. 71a — Cutler-Hammer Hand Motor Starter.
with the line to the motor armature will melt, but if the starting handle is moved
too slowly across the contact studs, the internal resistance coils will overheat and
perhaps burn out. The speed of acceleration of the starting handle can usually
be gauged by observing the speed of the motor armature. It should require no
more than 15 seconds to start the motors used in connection with wireless tele-
graph apparatus.
ARMATURE
1 10 VOLT D.C
Fig. 72 — General Electric Company's Hand Starter Connected to Shunt Wound Motor.
The release magnet M, Fig. 71, serves to protect the motor in case the main
line circuit is disconnected or should by accident the circuit to the motor field
windings be broken. In either event the handle H Hies back to the starting posi-
tion by the tension of a .spring attached to the bearing of the handle, and thus
interrupts the circuit to the armature.
60
PRACTICAL WIRELESS TELEGRAPHY.
The General Electric Company's hand starter differs slightly from the type just de-
scribed. A complete diagram is shown in Fig. 72 where the starter is connected to a simple
shunt wound motor. It is to he noted in this diagram that the release magnet M is shunted
across the D. C. line, and has a coil of fixed resistance R-l connected in series. In all
other respects, the wiring is the same as the first type and the starter performs the same
110 VOLT D.C.
Fig. 73 — Circuit of Automatic Starter for Marconi l/2 K. \V. 120 Cycle Set.
functions. If the source of power is cut off, magnet M releases the handle of the starter
whereupon it returns to the zero position, breaking the circuit to the armature.
56. Automatic Motor Starters. — It is c.ften essential to install a motor
generator at a point remote from the wireless cabin in order that the noise
from its operation may not interfere with the reception of wireless signals. In
instances of this kind automatic motor starters are employed, which are con-
trolled from a distant point by pressing a small button or closing a small switch.
Such starters possess the advantage that the acceleration of the starting handle is
uniform, and there is, therefore, no danger of burning out the armature or melt-
ing the fuses during the starting of a motor.
1 10 VOLT D.C
SHUNT
[AAAMAMJ J *!
D.C.
BRAKE RES.
VW\AM '
Fig. 74— Circuits of Automatic Motor Starter for Marconi ^ K. W. 500 Cycle Set.
There are numerous types of automatic starters on the electrical market but
only those used in modern Marconi sets can be given consideration here.
The complete circuit of the single step automatic starter is shown in the diagram of
Fig. 73. It is employed in connection with the l/2 K. W. 120 cycle Panel transmitters of
the Marconi Company. A single resistance unit R-l is connected in series with the brushes
MOTOR GENERATORS.
61
G and F of the armature. The solenoid winding S connected in shunt to the motor arma-
ture draws up the plunger C which in turn shunts the coil R-l through the contacts A and
B. When the main D. C. line switch is closed, current flows to the motor armature
through R-l and as the counter E. M. F. of the armature increases, the solenoid winding
becomes more strongly magnetized, drawing up the plunger, which cuts out the resistance
coil. Now when the plunger of the solenoid is in the full running position, contacts K and
L are forcibly opened and the resistance unit R-2 is connected in series with the solenoid
winding. This is to prevent the magnet winding from overheating and consequent injury.
The circuits of the automatic starter employed in the ^ K. W. 500 cycle transmitting
sets of the Marconi Company are shown in Fig. 74. When the starting switch 2 is closed,
the solenoid 3 is connected in shunt to the D. C. line. The flux from this solenoid attracts
the lever 4 making contact with points 5, thereby closing circuit from the D. C. line to the
motor armature through the resistance coil 6. Simultaneously the solenoid 7 is connected
in shunt to the D. C. line (through the lever 4) which attracts the lever 9 making contact
with point 10, thus cutting the resistance 6 out of the armature circuit, whereupon the
motor is connected directly to the main D. C. line. It is apparent that the lever of solenoid
3 opens and closes the main power circuit while the lever of solenoid 7 cuts out the re-
sistance in series with the motor armature. The solenoids 3 and 7 have the resistance coils
14 and 8 respectively, which are connected in series with their respective windings auto-
matically by the levers 4 and 9. These resist-
ances prevent the solenoid winding from over-
heating.
The automatic starter
also includes the ele-
ments of an electrodyna-
mic brake. When the
starting switch 2 is open,
•lever 4 drops back, also
lever 9, followed by con-
tact being made between points 11 and 12 con-
necting the resistance coil 13 in shunt to the
ttipJHBS * K^B motor armature and the series winding. The
pS§ fcj"4 1 lj|B| motor armature thus temporarily becomes a
i jpj generator and owing to the power expended in
tfS&BJ setting up a current through the resistance 13,
a powerful braking action is set up against the
armature, bringing it to a quick stop. The re-
sistance coil 15 is the motor field rheostat, by
means of which the speed of the motor can be
regulated over certain limits.
The starting switch 2 is usually one of the
snap type placed conveniently for the wireless
operator and near to the aerial changeover
switch. In some installations the starting circuit
opens and closes through the latter switch, stop-
ping the motor whenever the aerial switch is in
the "receiving" position. In case it becomes
necessary to install the motor generator in the
operating room, it is essential that the motor
stop immediately after the sending period, to
permit the reply from a distant radio station to
be deciphered without interference.
The circuits of the automatic starter
supplied with the 2 K. IV. 500 cycle transmitting sets of the Marconi Company are
shown in Fig. 75a. In addition to acting as a motor starter it performs the func-
tions of a main line circuit breaker through the medium of an overload relay
switch. The starter has three resistance units connected in series with the motor
armature instead of the single resistance unit described in the two previous types.
It will be observed from the drawing that the field winding of the motor is connected in
shunt with the D. C. line through the regulating field rheostat 23. As resistance is increased
at 23, the speed of the motor increases, and consequently, the frequency of the alternator.
Fig. 75 — English Marconi Company's one-half
Kilowatt Vertical Type Motor Generator with
Synchronous Disc Discharger on Shaft
62
PRACTICAL WIRELESS TELEGRAPHY.
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MOTOR GENERATORS.
63
The generator field winding is connected in shunt to the D. C. line through the low power
resistance 24 and the voltage regulating rheostat 25. The field circuit continues to the con-
tacts of the antenna switch 62 and 63 through the control switch 26 and finally to contact 5
of the automatic starter. By this connecion the circuit to the generator field winding re-
mains open until the bar 6 attached to the plunger A of the automatic starter has touched
point 5. When the bar of the automatic starter makes contact with point 4, the D. C. arma-
ture is connected directly to the main D. C. line.
By increase of resistance at the rheostat 25, the voltage of the A. C. generator drops but
it may be increased correspondingly by the reduction of resistance. Low values of voltage
may be secured at the terminals of the alternator by an external fixed resistance 24 con-
nected in series with the generator rheostat. This is shunted by the switch indicated in the
drawing.
The overload relay employed in conjunction with the automatic starter has the magnet
winding 20, which may be called the tripping magnet, and the second magnet winding 22,
which may be called the holding magnet. Winding 20 is in series with the D. C. armature on
the negative side of the line. If more than a predetermined number of amperes flow through
this winding, the lever 14 is drawn up, breaking the circuit of the solenoid winding 11
through the contacts 13 and 14. Immediately afterward the circuit through winding 22 is
closed through contacts 14 and 21. This causes the lever 14 to be held in that position until
either the main D. C. line switch or the starting switch 17 is opened.
SERIES
FIELD KA>1
RHEOS. ^V\
SHUNT \. ^
60 TO 500
CYCLES
110 VOLT D.C.
Fig. 76 — Hand Starter Connected to Motor Generator with Differential Motor Winding.
One terminal of the solenoid winding 11 is connected to the positive pole of the D. C. line
at point 12. The circuit continues through the fixed resistance 9, shunted by the switch 10,
through the contacts 13 and 14 of the overload relay, through contacts 15 and 16 of the
antenna switch, to a terminal of the winding 20, which is of negative polarity. Hence it is
readily observed that the solenoid winding is connected in shunt to the D. C. line when
either contacts 15 or 16 or the starting switch 17 is closed.
The switch 10 in shunt to the resistance 9 is automatically opened by the plunger A of
the automatic starter when it is in the full vertical or running position.
The resistance coils of the motor starter, connected in series with the D. C. line to the
armature, are progressively cut out of the circuit at contacts 1, 2, 3 and 4 by the bar 6. When
the circuit to the solenoid 11 is closed, the plunger A with the bar 6 moves in a vertical posi-
tion, the acceleration being regulated by a piston drawn through a vacuum chamber. When
contact is made between the bar 6 and point 1, the circuit to the armature includes the entire
set of resistance coils.
When the circuit to the winding 11 is interrupted, either at point 17 or at the serial
switch contacts 15 and 16, the plunger A drops downward and through the medium of con-
tacts 6 and 7, the resistance coil 8 is connected in shunt with the D. C. armature. At this
stage of operations the momentum of the armature causes it to become temporarily a D. C.
generator and current of large value flows for a few moments through the resistance 8. The
magnetic field* thus set up by the armature causes a powerful dragging action on the field
64
PRACTICAL WIRELESS TELEGRAPHY.
C-l
C-*
EARTH
Fig. 77 — Protective Condensers.
poles bringing the armature to a quick stop. Reviewing the foregoing: When the handle
of the type SH aerial changeover switch (or any other type) is thrown to a transmitting
position, the motor generator is automatically started, provided the main D. C. line switch
is closed. It will be brought to a quick stop when the antenna switch is placed in the receiv-
ing position, provided the switch 17 remains open. If the switch 17 is closed, the motor
generator can be kept in a continuous state of operation during the receiving period.
The speed of acceleration of the starter arm can be very closely regulated by means of
an adjusting screw attached to the bottom of the vacuum chamber. It usually requires 12
seconds to bring the starter up to the full running position.
When it becomes necessary to make repairs or adjustments to the generator or the A. C.
power circuits, the generator field switch 26 should be open. When the motor generator is
to remain idle for an indefinite period, the main D. C. line switch should be opened to break
the circuit to the field winding of the motor.
In the diagram of Fig. 76 the complete circuit of
a differentially wound motor coupled to a. simple
alternating current generator is shown, including the
connection of the field rheostats and the hand starter.
The student should give this diagram careful con-
sideration as it serves to show the complete funda-
mental circuit of various types of motor generators
in the Marconi service. This diagram should be
used in answer to the Government examination
query regarding the fundamental circuits of the
motor generator.
57. Protective Condensers. When a wireless
telegraph transmitter is in operation, a powerful
electrostatic field is set up in the region about the
aerial wires. // the power apparatus is installed in
such a manner that the low voltage wires leading to the motor generator or other
apparatus, lie parallel or in proximity to the antenna wires, currents of very high
potential will be induced in the power wires which may puncture the insulation.
A path is then afforded for the low voltage current which may cause an arc, com-
pletely short-circuiting the windings of a motor generator. In other words, this
induction sets up a difference of potential between
the various windings or between the windings and
the frame of a motor generator which may result
in a disastrous burnout. The low voltage wires
can be well protected by installing them in iron con-
duit, the latter in turn, being thoroughly connected
to the earth. The induced currents will flow on
the surface of the pipe and be neutralized by the
earth connection, and thus do no harm to the power
wiring. The power wires of commercial radio in-
stallations are either installed in iron conduit or in
lead-covered cables, but in addition to this protec-
tion, protective devices known as protective con-
densers or protective resistances are employed.
Protective condenser units consist of two one-half
microfarad condensers connected in series mounted on an insulating support as in Fig. 77.
The middle connection is extended to the earth and the remaining terminals connected
across the field or armature windings of a motor generator or between these windings and
the frame. Differences of potential that may be induced in such windings are thereby
neutralized and reduced to zero through the earth connection.
Carbon or graphite rods of high resistance are often employed for protective purposes
as shown in Fig. 78. A single graphite rod having resistance of about 5,000 ohms is mounted
on an insulating support and connected to earth at the middle point. The two remaining
terminals are connected to the windings of the motor generator to be protected. These rods
EARTH
Fig. 78— Protective Resistance Rod.
MOTOR GENERATORS.
65
— PRO COND
have sufficient resistance to prevent appreciable leakage of the low voltage current but
possess sufficient conductivity to pass the induced current of high voltage.
Protective rods or protective condensers are connected :
(1) In shunt to the motor armature.
(2) In shunt to the generator armature.
(3) In shunt to the field windings of the motor.
(4) In shunt to the field windings of the generator.
The diagram of Fig. 79 shows how protective condensers are attached to the motor gen-
erators in modern Marconi sets. Condensers A, B, C and D are of l/2 or 1 microfarad ca-
pacity each. One terminal is connected to a
binding post and the other terminal to
the frame of the motor generator. The
frame of the motor generator is connected
to the earth at binding post E or at any
other convenient point. These condensers
are generally mounted in a containing rack
on the top of the motor generator and pro-
tected from injury by a cast iron case.
In naval radio systems, fuses are con-
nected in series with the protective con-
densers to protect the power mains in case
of puncture of the dielectric.
58. Care of the Motor Generator.
—When first coming in contact with a
motor generator of any type, the stu-
dent should note particularly how the
brushes are held in the rocker arm and
how the connections are attached to
and between the various brush holders.
He should also note the connections
inside the frame from the motor to
the generator. Particular observance
should be made of the thrust bearing
mounted on the end of the shaft to
take up the "end play." In the case of
the 2 K.W 500 cycle motor generator, Fig- 79-
the method of attaching the rotary
spark gap to the end of the generator shaft should be carefully gofte over.
Proper care of the motor generator is assured if the following general rules
are observed:
(1) Keep motor brushes clean and free from carbon dust. Use sand paper only,
avoid emery cloth.
(2) Clean commutator occasionally with a fine grade of sand paper.
(3) Oil bearings frequently. Open up petcocks occasionally, to assure that oil
container has the necessary supply.
(4) Make sure that all petcock valves are tight so that they will not loosen by
vibration.
(5) Wipe off frame of motor generator, brush holders, and rocker arm occa-
sionally to prevent accumulation of carbon dust and grease.
(6) Do not overspeed motor. Normal speed can be observed by the reading of
the frequency meter or by applying a speed indicator to the end of the
motor generator shaft. Observe either wattmeter or ammeter occasionally
to insure that the normal load of the generator is not exceeded.
(7) When removing armature from motor generator, it is generally more con-
venient to take off the generator end plate.
(8) Be careful not to injure commutator by scraping against the field poles.
(9) See that protective condensers are at all times properly connected.
(10) Punctured condensers should be removed or disconnected from the circuit.
H^rc^f^rCGelTteorrS,are C°"
66
PRACTICAL WIRELESS TELEGRAPHY.
(11) In the case of the 2 K. W. 500 cycle motor generator, adjust overload
relay for 35 amperes.
(12) If a single resistance coil in either the hand starter or the automatic starter
burns out, close the circuit by placing a jumper around the burned out
portion.
(13) If field rheostat burns out, close the circuit by a jumper. If burned beyond
repair, substitute 3 or 4 16 C. P. lamps, connected in parallel.
(14) Tighten up all connections frequently. These should be gone over once
per month.
59. How to Remove Motor Generator Armature. — In case it becomes
necessary to remove the armature of the 2 K. W. 500 cycle motor generator for the purpose
of repairs, it is necessary first to remove the casing of the spark gap. Follow this by taking
Fig. 79a — 1 K. W., 60-cycle Motor-generator (Two Bearing L'niu.
out the wedge-shaped key in the end of the generator shaft. If the rotary disc is given a
slight tap with the hammer, the key will be released and the disc may be removed from the
shaft. After this, the bearing bracket can be removed from the generator end. The brushes
should then be removed from the commutator and the collector rings. After these operations
have been gone through, the armature can be pulled out and a new one inserted, if necessary.
When the armature is replaced, the oil rings should .be held up to permit the shaft to pass
through the bearings. Care should be taken to' see that the oil rings are working properly
and that the bearings are thoroughly oiled for the initial test. Before starting the motor
generator careful inspection should be made to see that all parts are properly secured and in
working order.
It should be noted that the mica of the commutator of this machine is undercut about 1-32
inch, and before it gets flush with the commutator bars, the mica should be cut out again.
PART V.
STORAGE BATTERIES AND CHARGING
CIRCUITS.
60. THE NECESSITY FOR A STORAGE BATTERY IN A RADIO INSTAL-
LATION. 61. GENERAL CONSTRUCTION AND ACTION. 62. THE
CHARGING PROCESS. 63. THE FUNDAMENTAL ACTIONS OF A
STORAGE CELL. 64. THE ELECTROLYTE. 65. THE HYDRO-
METER. 66. How THE CAPACITY OF A STORAGE CELL Is RATED.
67. FUNDAMENTAL FACTS CONCERNING THE STORAGE CELL.
68. How TO CHARGE A STORAGE CELL. 69. How TO DETERMINE
THE VALUE OF THE CHARGING RESISTANCE. 70. LAMP BANK
RESISTANCE. 71. THE USE OF THE AMMETER AND THE UNDER-
LOAD CIRCUIT BREAKER. 72. THE AMPERE HOUR METER.
73. OVERCHARGE. 74. How TO CHARGE A BATTERY WHEN THE
VOLTAGE EXCEEDS THAT OF THE CHARGING GENERATOR.
75. How TO DETERMINE THE POLARITY OF THE CHARGING GENE-
RATOR. 76. DETERMINATION OF THE STATE OF CHARGE AND
DISCHARGE OF A BATTERY. 77. KEEPING THE LEVEL OF THE
ELECTROLYTE. 78. PROTECTING THE CE^LS FROM ACID SPRAY.
79. GENERAL INSTRUCTIONS FOR THE PORTABLE CHLORIDE TYPE
OF ACCUMULATORS. 80. GENERAL OPERATING INSTRUCTIONS
FOR THE EXIDE CELL. 81. TlIE EDISON STORAGE BATTERY.
82. THE CHARGE AND DISCHARGE OF THE EDISON CELL.
60. The Necessity for a Storage Battery in a Radio Installation. — The
International Radio-Telegraphic regulations require that an auxiliary source of
direct or alternating current be available for operation of the motor generator or
a low powered emergency transmitter in case of an accident to a vessel at sea
which might put out of action the ship's generator.
The United States regulations (Act of August 13, 1912) require that the
auxiliary radio transmitter be capable of transmitting to a distance of 100 miles.
A small A. C. or D. C. generator operated by a gasoline or oil engine is permissi-
ble as a source of current supply under the United States statute, but the general
custom is to employ a battery of storage cells for direct operation of the motor
generator or emergency transmitter.
Two general types of storage cells are used in connection with emergency
transmitters — the lead plate, sulphuric acid cell such as the "chloride" and "exide"
types manufactured by the Electric Storage Battery Company and the Edison
nickel iron-alkali cell. Certain fundamental facts concerning the charge and dis-
charge of storage cells and the standard circuits for their use will now be con-
sidered, which is to be followed in another chapter (Part X) by a complete de-
scription of the charging panels employed in commercial marine radio instal-
lations.
68 PRACTICAL WIRELESS TELEGRAPHY.
61. General Construction and Action. — It is not really electricity which
is stored up in a storage cell, but the flow of current from a direct current dynamo
through the cell from plate to plate performs a certain amount of chemical ivork.
Whenever required this stored up chemical energy can be released in the form of
an electric current which will pass from plate to plate through an external circuit.
The common type of lead cell comprises a set of prepared lead plates immersed
in a dilute solution of sulphuric acid, but a certain electrochemical process known
as "charging" must be gone through in order that the cell may deliver a current
of electricity.
There are two general methods by which the lead plates for a storage cell
may be prepared :
(1) A paste of litharge or oxide of lead mixed with a dilute solution of sulphuric
acid may be applied to perforations in a lead grid, and then by means of a
current of electricity and a suitable electrolyte the surface of some of these
plates may be coated with peroxide of lead while other plates become simply
spongy.
(2) Large lead plates may be immersed in a certain electrolyte and connected
to the terminals of a dynamo. By repeated charge and discharge, some of
the plates may be coated with peroxide of lead while the others simply be-
come spongy.
Reviewing the development of the storage battery, we find:
(1) That the earlier types of storage cells comprised two lead plates immersed
in a dilute solution of sulphuric acid. The terminals of the plates were con-
nected to a direct current dynamo for a period of several weeks. By repeated
charges and discharges, the surface of the plates received a coating of
so-called "active material."
(2) Later it was determined that the formation of the plates could be hastened
by chemical means previous to the charging process and the manufacture
of the plates was accordingly cheapened.
(3) In certain types of present day cells, for instance, the exide lead cell, the
active material is applied to the plates mechanically, in the form of a paste.
62. The Charging Process. — In general the charging process of a storage
cell is as follows :
When two ordinary lead plates or sets of plates are placed in a dilute solution of sulphuric
acid of the correct proportion and a direct current of electricity from a dynamo passed from
one plate through the solution to the other, the resulting chemical decomposition deposits a
coating of peroxide of lead on one plate while the other plate becomes gray and spongy or
porous. When one set of plates is fairly well coated with lead peroxide and the other set
becomes spongy, the cell is said to be "charged." If the terminals of these plates are now
joined together by a conductor (the charging generator having been disconnected), a cur-
rent of electricity will flow from plate to plate.
The plate coated with lead peroxide is known as the positive plate of the storage cell and
the other, the negative plate. When joined together by a copper conductor, current flows in
the external circuit from the positive to the negative plate and the resultant chemical change
undoes the work of charging, e. g., part of the peroxide of lead of the positive plate and the
active material on the negative plate is converted to lead sulphate which covers the surface.
When the plates are fairly well coated with sulphate, the cell is said to be discharged. In
order that current may be drawn from the cell again, the plates must be connected to a
source of direct current and the charging process repeated.
The processes involved in the charge and discharge of storage cells may be
better understood from the explanation given by the Electric Storage Battery
Company in the following paragraph.
63. The Fundamental Actions of a Storage Cell. — When a lead storage
cell is put on discharge, the current is produced by the acid of the solution going into and
combining with the porous part of the plate called "active material." In the positive plate, as
stated before, the active material is lead peroxide and in the negative plate it is metallic lead
in a spongy form.
STORAGE BATTERIES AND CHARGING CIRCUITS.
69
When the sulphuric acid in the solution combines with the lead in the active material, a
compound known as "lead sulphate" is formed.
As the discharge progresses, the solution becomes weaker by the amount of the acid used
in the plate, which incidentally produces the compound of acid and lead called "lead sulphate."
This sulphate continues to increase in quantity and bulk, thereby filling the pores of the plate.
As the pores of the plate become filled with sulphate, the free circulation of acid in the plate
is retarded, and since the acid cannot then get into the plate fast enough to maintain the
normal action, the battery becomes less active, as is indicated by a rapid drop in voltage.
During the charging period direct current must pass through the cells in the direction
opposite to that of discharge. This current will reverse the action which took place in the
cells during discharge. It will be remembered that during discharge the acid of the solution
went in and combined with the active material, filling its pores with sulphate and causing the
solution to become weaker. Reversing the current through the sulphate in the plate restores
the active material to its original condition and returns the acid to the solution. Thus, dur-
ing charge, the solution gradually becomes stronger as the sulphate in the plate decreases,
until no more sulphate remains and all the acid has been returned to the solution, when it
will be of the same strength as before the discharge and the same acid will be ready to be
used over again during the next discharge. Since there is no loss of acid by this process,
none should ever be added to the solution.
The whole object of charging therefore is to drive from the plates the acid
which if now absorbed by them during discharge.
64. The Electrolyte. — The liquid in a storage cell is known as the elec-
B
ELECTROLYTE
trolyte which in the case of the lead cell is a 20 per cent,
solution of sulphuric acid. It is important to have the
electrolyte of the right strength or the cell will not func-
tion properly. The strength of the electrolyte or the
proportion of the acid to water is expressed in terms of
specific gravity.
The specific gravity of a compounded solution is a
measure of its density or weight as compared to that of
chemically pure water. If water be taken as unity (or 1)
it is found that certain compounded solutions of acid,
etc., are heavier than water by a certain amount. Thus
the specific gravity of the electrolyte of one type of lead
plate stofage cell is approximately 1.215, meaning that if
a cubic centimeter of water weighs one gram, one cubic
centimeter of the electrolyte weighs 1.215 grams. It is,
therefore, evident that the greater the proportion of the
acid in the electrolyte of a storage cell, the higher will be
the reading of the specific gravity.
65. The Hydrometer. — The gravity of the solu-
tion of a storage cell is measured by an instrument known as a
hydrometer, B. sketch of which is shown in Fig. 80. The long
glass rod A-B has the bulb at one end loaded with shot or mer-
cury. When dropped into a solution of acid it sinks to a certain
depth, depending on the weight of the liquid. If placed in chem-
ically pure water, the hydrometer would sink to the bottom or at
least below the level of the liquid, but if it is placed in a dilute
solution of sulphuric acid, a part of the tube protrudes above the
surface. The reading of the hydrometer scale at the surface of
the solution is a measure of the specific gravity. The specific
gravity of the chloride portable storage cell varies between 1.205
and 1.215 and for the various exide cells between 1.280 and 1.300.
66. How the Capacity of a Storage Cell Is Rated. — The capacity of a
storage cell is rated in amperehours. The amperehour is the unit employed
to express the equivalent quantity of current represented by current of one
ampere flowing through a given circuit for an hour of time. The storage
cells used with commercial radio sets are rated at 60 to 224 ampere hours
WA
Fig. 80 — The Hydrometer.
70
PRACTICAL WIRELESS TELEGRAPHY.
capacity according to the power of the particular installation. The cells of
larger capacity are used for auxiliary lighting service as well as for operation
of the radio-transmitter.
A clearer interpretation of the practical application of the term amperehour as applied
to the rating of storage cells may be obtained from the following explanation. For ex-
ample, the chloride type of cell is rated on an 8 hour basis and the exide cell on a 4 hour
basis. Thus if the chloride cell is rated as having capacity of 60 amperehours, the normal
discharge rate is determined by simply dividing the rating 60 by 8 or 7^ amperes, which is
the normal current is amperes to be taken from the cell during discharge, and in the same
manner the normal discharge rate of a 60 amperehour exide cell is found to be 15 amperes.
The normal discharge rate of the chloride lead cells (in use in the Marconi Service) is also
the normal charging rate, but different charging rates are given for the exide lead cell
according to the rated capacity of the battery. Generally at the beginning, the batteries are
charged at a heavy rate, but as the charge progresses the charging current is reduced.
VOLTAGE
REGULATOR
Fig. 81 — Simple Charging Circuit.
67. Fundamental Facts Concerning the Storage Cell. The student should
bear in mind certain facts concerning the storage cell :
(1) It has low internal resistance and therefore delivers a very strong current.
(2) The flow of current is more lasting than in the ordinary types of primary
cells.
(3) The "charging" process requires considerable time — a matter of hours to
convert the surface of the plates to so-called "active material."
(4) During the charging period, a stated number of amperes must pass
through the cell — the actual value being designated by the maker.
(5) A normal rate of discharge is given by the manufacturers which must not
be exceeded except in special types.
(6) The fully charged voltage of the lead cell averages 2.1 volts on open
circuit, values as high as 2.5 or 2.6 volts being obtained with the charging
current flowing.
(7) The lead cell is said to be discharged when the voltage of the individual
cell falls to 1.7 or to 1.8 volts provided the reading is taken at normal
rates of discharge current.
(8) The fully charged voltage of the Edison cell is 1.2 volts.
(9) The Edison cell is said to be discharged when the voltage of the cell, at
normal discharge rates, falls to .9 volts.
(10) The Edison cell and the lead cell differ both in material, general con-
struction, and electrolyte.
68. How to Charge a Storage Cell. — A storage battery is "charged"
by connecting the positive terminal of the battery to the positive terminal of a
direct current dynamo, and the negative terminal of the battery to the negative
terminal of the dynamo, but a resistance or regulating rheostat must be connected
in series with the charging circuit, otherwise, an excess of current will flow and
the battery and perhaps the generator put out of commission. This is due to the
fact that the storage cell possesses very low internal resistance.
An elementary charging circuit is shown in Fig. 81 where the brushes of the generator
STORAGE BATTERIES AND CHARGING CIRCUITS.
71
E, E, are connected to the positive and the negative terminals of a 30 volt battery with a
regulating resistance R connected in series. The resistance of R varies as the normal charg-
ing rate of the particular battery under charge, from 5 amperes in the smaller types of cells
to 50 or 100 amperes in the larger types. The resistance coil may be of fixed or variable
value. It is sometimes fitted with a single blade switch, permitting a portion of the coil to
be short circuited, to provide two values of charging current. It is made up of a resistance
wire alloy, constructed to withstand continuous flow of current at the normal rating of the bat-
tery without overheating.
When the circuit from the charging- generator is closed, current flows from
plate to plate through the electrolyte until the surface is converted to "active
material," the process requiring several hours, according to the degree to which
the cell has been discharged. In any case the charging should continue until
there is no further rise in either the specific gravity or the voltage.
mm
LAMPS
Fig. 82 — Diagram of Simple Charging Circuit Including Lamp P>ank "Resistance and Underload Circuit
Breaker.
It should be kept in mind that THE VOLTAGE OE THE CHARGING
DYNAMO MUST ALWAYS EXCEED THE MAXIMUM VOLTAGE OE
THE STORAGE BATTERY BECAUSE THE VOLTAGE OF THE BAT-
TERY EXERTS A BACK PRESSURE OR COUNTER E. M. F. ON THE
CHARGING SOURCE AND IF THE VOLTAGE OF THE DYNAMO IS
LESS THAN THAT OF THE BATTERY THE LATTER WILL NOT BE
CHARGED.
69. How to Determine the Value of the Charging Resistance. — The resist-
ance of the series charging rheostat for a given battery may be determined by
Ohm's law. Assume that the battery, Fig. 81, has, when fully charged, a voltage
of 30 volts, that the normal charging rate as given by the manufacturer is 6
amperes and the voltage of the generator 110 volts; then the battery exerts a
back pressure of 30 volts on the generator and the net effective voltage is 110 -
30 volts or 70 volts.
For ordinary direct current circuits according to Ohm's law,
R=^
I
hut in this case the value of R is determined by
E-e
R =-
I
where E — the voltage of the charging generator,
e - the fully charged voltage of the battery,
I - the normal, charging current as given by the manufacture.
Then in the example cited,
110 — 30
R =11.6 ohms.
72
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 83 — Motor of Ampere Hour Meter,
70. Lamp Bank Resistance. — A bank of 16 or 32 C. P. lamps are frequently
employed to adjust the flow of current through a battery undergoing charge. A circuit of
this type is indicated in Fig. 82. Since the resistance of the battery is small compared to
that of the lamps, the flow of current through the cells is governed by resistance of the
lamps.
A 16 C. P. incandescent lamp having a carbon filament passes y2 ampere under an E. M. F.
of 110 volts hence 15 such lamps connected in parallel will pass 7l/2, amperes, about the
correct value for the smaller types of lead cells. The strength of the charging current can
be regulated in small steps by turning on or off a certain number of lamps.
71. The Use of the Ammeter and the Underload Circuit Breaker. — To per-
mit the charging current to be carefully regulated, the charging circuit should
include an ammeter as at A, Fig. 82.
A very important protective mechanism for a storage battery charging circuit is an
underload circuit breaker. The function
of this breaker is to open the charging line
when the voltage of the charging generator
falls below the voltage of the battery. The
battery is thus protected from discharge in
case the charging generator is stopped
without first disconnecting the batteries. A
very simple type of underload breaker used
on the small panel sets of the Marconi
Company is shown in Fig. 82. A solenoid
winding W is connected in series with the
charging circuit and carries the full value
of the charging current, the resulting flux
acting upon the plunger P which carries
the crossbar and the copper contacts S-l
and S-2.
When pushed up by hand, plunger P
closes the circuit from the charging generator to the battery. The winding W is thus magne-
tized and holds the iron plunger in this position until the charging circuit is actually interrupted
or the voltage of the generator falls below the battery. In event of either happening, the
plunger drops downward, breaking the circuit.
72. The Ampere-Hour Meter.
A particularly useful instrument
for denoting the state of "charge"
or "discharge" of a storage battery
is the ampere-hour meter, which in CURRENT
essence is a specially constructed
small motor connected in series
with the charge and discharge of a
storage battery.
The motor is geared to a pointer
moving Over a dial Calibrated in FI'R. 84— Sketch Showing the Direction of Fluxes in
ampere hours, and therefore per- Ampere Hour Meter Motor'
mits a direct reading of the quantity of current flowing during the discharge of a
storage cell.
A diagram of the motor of the Sangamo ampere hour meter is given in Fig. 83.
It consists of a copper disc D, floated in a pan of mercury between the poles of a
permanent magnet to which current is lead by the contacts C-l, C-2. The current of
electricity enters the contact C-l, passes through the comparatively high resistance
mercury H, to the edge of the low resistance copper disc P, across the disc to the
mercury H, and out at contact C-2. The magnetic flux cuts across the disc on each
side from N to S, making a complete circuit through M-l and M-2. The relative
directions of the magnetic flux and the current of electricity as well as the resulting
motion are shown in Fig. 84.
According to the laws of electromagnetic induction, if a current-carrying conductor cuts
a magnetic field at right angles, a force is exerted upon the conductor tending to push it
CURRENT
STORAGE BATTERIES AND CHARGING CIRCUITS.
73
at right angles to both the current and the flux; hence the disc of the meter revolves at a
uniform rate.
When fitted with an eddy current damper or generator which requires a driving force
directly proportional to the speed of rotation, the mercury motor generator becomes a
meter. The speed of such a meter is a measure of the current or the rate of flow of the
electricity through the motor element and each revolution of the motor corresponds to a
given quantity of electricity. Then by connecting a revolution counter to this motor gen-
erator we have a means of recording the total quantity of electricity in ampere hours that
is passed through the meter.
CIRCUIT BREAKER WITH
TRIPPING MAGNET
TO LOAD
Fig. 85 — Fundamental Charging Circuit with Overload and Underload Circuit Breaker and Ampere
Hour Meter.
During discharge of a storage battery the pointer of the ampere hour meter
moves from the zero position of the scale in a clockwise direction toward the full
scale reading, but when the battery is placed on charge the pointer moves in a
counter-clockwise direction toward the zero division of the scale. When it
has reached this point, the contacts A and B Fig. 85, are closed and the circuit
breaker is tripped by the no voltage release magnet M. This cuts off the charg-
ing current. Current flows through winding M only during the time required
to throw the breaker, the current being turned off automatically, through a set
of contacts, by the breaker armature. The circuit for the no-voltage release
magnet is closed when the circuit breaker proper is set by hand.
Fig. 85 is a fundamental diagram of a charge and discharge circuit of a storage battery
installation having a Sangamo ampere hour meter. The meter is connected in the circuit
in such a way as to indicate the quantity of current taken in by the battery during the
charging period and that taken out by the motor generator or auxiliary lights on discharge.
74
PRACTICAL WIRELESS TELEGRAPHY.
The direction of the current through the ampere hour meter on discharge is opposite to
that when the battery is on ''charge," hence fye movement of the motor is reversed accord-
ingly.
For sake of clearness the necessary switches for placing the battery on charge or dis-
charge have been omitted.
The short arrows, Fig. 85, indicate the direction of the charging current while the bat-
teries are on charge and the long arrows indicate the direction of current during discharge.
This diagram is not intended to convey a description of the mechanical construction or
operation of the circuit breaker, but merely serves to show the complete fundamental charg-
ing circuit.
73. Overcharge. — Theoretically we should be enabled to draw the same
quantity of current from a storage
battery upon discharge as put into
it on charge, but practically this
cannot quite be done. The plates
of the battery must be given an
occasional overcharge to keep them
in good working condition, that
is, there must be put into the bat-
tery under normal conditions a
greater quantity of current than is
taken out of it. Ampere hour
meters are constructed to take care
of the required overcharge auto-
matically by a device known as a
resistor which cannot be explained
in detail here. Briefly it causes the
pointer of the ampere hour meter
to move to the zero position of the
scale from a given higher reading,
at a slower rate than that which
brought it to the maximum reading
thus giving the requisite overcharge. But with all this, the readings of the ampere
hour meter can not quite keep pace with the state of the storage battery, hence, it
is necessary from time to time to move the pointer of the ampere hour meter from
the zero position to a reading corresponding to from 20 to 50 ampere hours,
after which the battery is placed on charge until the pointer again returns to the
zero position.
74. How to Charge a Battery when the Voltage Exceeds that of the Charg-
ing Generator. — As mentioned in a previous paragraph, the voltage of the
charging generator must exceed the combined fully charged voltage of the cells.
Since the auxiliary battery for a radio set consists of 60 cells, and their voltage
combined is 126 volts, they cannot be charged in series from a 110 volt source of
direct current. The battery must be split into two units of 30 cells each, which
are connected in parallel and finally to the terminals of a charging generator, but
on discharge the cells are connected in series.
A completely satisfactory diagram of this connection appears in Fig. 86, where the four-
blade switch, when thrown to the "charge" position, connects battery A and battery B in
parallel, but in the discharge position reconnects them in series giving approximately 126
volts for the operation of a standard motor generator. This diagram shows (1) the position
of the charging resistance and the underload circuit breaker in the charging circuit, (2)
the voltage of the generator, (3) the voltage of the individual battery units and (4) the
final discharge voltage of the cells. The charging dynamo in the case of a marine radio
installation is the ship's generator, which is situated at some point in the ship's engine room.
It has been mentioned that two values of charging current are employed for the exide
type of cells, a heavy value for the start of the charge and a lesser value at the completion
of the charge, but no special appliances are fitted to the Electric Storage Battery Company's
Fig. 85a— Portable Exide Storage Cell, Supplied with
Marconi Emergency Sets.
STORAGE BATTERIES AND CHARGING CIRCUITS.
75
76
PRACTICAL WIRELESS TELEGRAPHY.
NE6AT!V£
PUTC
ship's charging panel whereby the.se two values can be obtained. The flow of charging
current is automatically taken care of by the battery, the counter E. M. F. of which rises
as the charge progresses. This gradually reduces the charging current without extra
appliances.
75. How to Determine the Polarity of the Charging Generator. — We have
mentioned that during charge the
positive pole of the storage bat-
teries must be connected to the
positive pole of the dynamo.
The polarity of the charging
mains may be determined in three
ways:
(1) By a direct current voltmeter of
the magnetic type;
(2) By an electrochemical polarity
indicator;
(3) By dipping the terminals of the
dynamo in a glass of plain or
salt water.
Direct current voltmeters with
magnetic mechanism have a (-J-) and
( — ) mark on the binding posts. If
connected improperly to a source of
direct current the pointer instead of
swinging in the direction of the full
scale position will move to the left of
the zero position, but when connected
properly, the pointer moves from left
to right. The wire of the dynamo
Fig. 86a— Detail of Exide 11 M. V. Storage Cell. connected to the (+) binding post
of the voltmeter is the positive wire and the other, of course, the negative wire.
Chemical polarity indicators have a solution of iodide of potassium mixed with starch
sealed in a glass tube provided with terminals. When connected to the terminals of a
charging line, current flows through the liquid and decomposes the solution, turning the
positive terminal of the tube blue.
The polarity of the charging source may be ascertained by dipping the terminals of a
D. C. line in a glass of plain water as in Fig. 87 or
preferably salt water. Bubbles will appear at the nega- VWfflMfljfc 4"
tive terminal of the line. The negative wire should be
connected to the negative pole or terminal of the
battery.
76. Determination of the State of Charge
and Discharge of a Battery. — The following
instructions apply to the lead plate cell. It is
not difficult to determine the state of charge and
discharge of a storage battery if the circuit in-
cludes an amperehour meter. To illustrate the
utility of this instrument, assume a 60 ampere-
hour battery which is being discharged through
the windings of a motor generator. Fully
BUBBLES
charged, the pointer of the amperehour meter Fig. 87— Method of Determining the
rests at zero but as the discharge, progresses the
pointer gradually moves in a clockwise direction and if it then rests at 40, it is an
indication that 40 amperehours of current have been taken from the battery
which, of course, is not completely discharged. In order that the battery may be
ready always for emergency use, the changeover switch on the charging panel
should be immediately thrown to the "charge" position, the underload circuit
breaker closed, whereupon the pointer of the amperehour meter will, as the charge
progresses, move counter clockwise or towards the zero position of the scale which
STORAGE BATTERIES AND CHARGING CIRCUITS. 77
when attained throws off the charging current automatically by means of the
no voltage release magnet attached to the underload circuit breaker.*
In event the equipment is not fitted with an amperehour meter, the full
charged condition of the chloride cell may be determined, by charging at normal
rates for two hours after gassing begins and for the exide cell, one hour after
gassing begins.
Each cell should then indicate 2.08 volts on open circuit and the gravity of the
solution should have reached a maximum value.
The operator should understand that a storage cell is considered to be fully
charged when during charging there is no further rise in either gravity or voltage ;
and that in any case a maximum value of voltage and gravity should be aimed for
rather than a final value.
The state of a storage battery may be obtained in another way by placing it
on discharge at normal rates and observing the reading of the voltmeter with the
current flowing. If the reading per cell is less than 1.8 volts, the battery should
be placed on charge immediately. It should be kept in mind that the specific
gravity of the electrolyte falls on discharge and rises on charge, hence a hydro-
meter may be used in place of the amperehour meter for determining the condi-
tion of a cell but the amperehour meter is the most convenient for the purpose.
In large isolated battery units, a temperature correction table is given to permit changes
in temperature to be accounted for when taking readings of the specific gravity, but such
tables are not furnished for the battery sets employed in marine radio sets.
77. Keeping the Level of the Electrolyte. — There is no loss of electrolyte
in the charge or discharge of a battery, except the loss due to spraying. The acid does
not evaporate but the water does. Hence from day to day enough water must be added to
keep the electrolyte at a level of ]/2 to 24 inches above the plates.
Replenishing of the water is more important and must be attended more frequently in
hot climates than in temperate zones.
78. Protecting the Cells from Acid Spray. — At the completion of a charge,
all cells should be thoroughly wiped off first with a damp cloth followed by a dry cloth.
Surface leakage of the current is thus prevented.
The cells should also be protected from salt spray, the accumulation of dirt and dust,
etc. Contacts and connections must be kept scrupulously clean and should be thoroughly
examined from time to time.
79. General Instructions for the Portable Chloride type of Accumulators.
—The following instructions apply to the portable "chloride" accumulator of the
Electric Storage Battery Company :
The proper polarity having been obtained, charge the battery at the rate given on the
name plate until there is no further rise in the voltage of each cell of the battery and each
cell has been gassing or bubbling freely for at least two hours and there is not further rise
in the specific gravity of the electrolyte over the same period.
If the temperature of the electrolyte rises to 100 deg. Fahrenheit during the charge, the
current should be reduced or stopped until it lowers.
The voltage at the end of the charge may be between 2.4 and 2.6 volts per cell, depend-
ing on their temperature and age.
The higher voltages are obtained on new batteries with low temperature ; on all bat-
teries at high temperatures, the lower voltages are obtained.
It therefore must be understood that in determining the completion of a charge, a fixed
or definite voltage is not to be considered, but rather a maximum voltage as indicated by
there being no further rise in the voltage over a period of two hours. It is of the utmost
importance that the charge be complete.
Great care must be taken not to bring a naked flame near the openings in the top of the
battery during or immediately following a charge.
The proper specific gravity of the electrolyte at the end of charge is 1.210, but a varia-
tion of from 1.205 to 1.215 is allowable.
*As already explained the battery must be given a small overcharge occasionally and therefore
when the pointer has returned to the zero position, it is moved by hand to point IS or 20 (or possibly higher
depending upon the capacity of the battery) the battery being again placed on charge until the pointer returns
to the zerp po$ition.
78 PRACTICAL WIRELESS TELEGRAPHY.
Do not adjust the specific gravity except when the battery is fully charged.
In ordinary use, there is no occasion to adjust the electrolyte of the cell oftener than
once in every three or four years.
After adjusting, charge for an hour in order to thoroughly mix the liquid just added
with the electrolyte.
By all means do not add electrolyte until it is determined that the specific gravity can-
not be brought up to the proper point by charging.
The sediment which gradually accumulates in the bottom of the jars must not be
allowed to touch the bottom of the plates as if it does serious injury may result. It is
best to overhaul the cells and remove the sediment at least once a year.
If the battery is not to be used for a considerable period, care should be taken that it
is charged once every two months and that the plates are kept covered by regularly adding
water.
If it is not possible to charge at least once every two months, the battery may be taken
entirely out of service as follows : Fully charge the battery, remove the vent caps, pour
out the electrolyte by turning the case upside down, fill with fresh, pure water and allow
to stand 12 or 15 hours. Then pour off the water, wipe the case dry, grease the terminals
and the battery can stand indefinitely.
80. General Operating Instructions for the Exide Cell. The following
instructions apply specifically to the Exide cells supplied to marine radio sets,
particularly the 60 cell M. V. 11 type. (E. S. B. Co.)
Keep the level of the electrolyte always above the top of the plates by replacing evapora-
tion with pure, fresh water (never anything else) to a height of one-half inch (not more)
above top of plates. The best time for adding water is just before a charge. Do not use
metallic receptacles for holding the water.
Keep flames of all kinds (match, candle, lantern, cigar, etc.) away from battery at all
times.
Battery is to be "floated" at all times, except when charging or discharging. When
floating, both lamps on battery switchboard will burn dimly. If either lamp goes out,
immediately replace it with another of same rating.
Twice each month, preferably when in port, charge the battery by opening the 6 pole
switch, closing the circuit breaker, and again closing the 6 pole switch to the charge side.
Move the needle of the ampere hour meter back to about 50 and charge until the pilot cell
gravity and the voltage of each side have remained constant for one hour and all cells
have been gassing or bubbling freely for the same length of time. This means that, under
normal floating conditions, the charge will be of about one and one-quarter hours' dura-
tion. After the charge reset the needle of the ampere hour meter to zero. Raise the cover
of the battery box during this charge.
After a discharge of any kind immediately put the battery on charge and continue the
charging until the needle of the ampere hour meter has returned to zero.
In order to check the generator polarity and to guard against the battery becoming
accidentally discharged through the reversal of the generator, read the voltmeter irequent^.
with the voltmeter plug in openings marked "Bus."
If the polarity has changed, throw over the switch marked "Reversing Switch."
Before the semi-monthly charge, read and record the specific gravity of each cell of the
battery.
On the day of the semi-monthly charge, after the charge has been completed, read and
record the specific gravity of the pilot cells.
On other days read and record the specific gravity of the pilot cells at the same time
each day. These readings will indicate the state of charge of the battery and will be a
check on the "Floating."
On the semi-monthly charges the vent plugs should be replaced after charges are com-
pleted.
If the gravity of any cell shows a marked falling off relative to the rest of the cells,
promptly investigate the cause and correct it.
If a jar develops a leak, promptly replace it.
If a cell becomes "dead" from a leaky jar, cut it out of circuit by opening up the con-
nector and restore the circuit with a jumper.
When charging, keep the bus voltage at 110 volts, as if it is low the charging rate will
be reduced and the time required to charge correspondingly increased.
Keep everything about the battery clean and dry.
STORAGE BATTERIES AND CHARGING CIRCUITS. 79
Keep terminals and connections tight and free from corrosion.
Do not allow any impurities to get into a cell.
81. The Edison Storage Battery. — The Edison cell differs from the lead
cell both in the construction of the plates and the electrolyte. The active mate-
rials of this cell are iron oxide and nickel hydrate. The electrolyte is a 21 per
cent, solution of potassium hydrate mixed with a small amount of lithium
hydrate.
The negative plate consists of a nickel-plated steel grid, into the pockets of which are
hydraulically pressed, perforated, corrugated steel pockets which have been filled and
packed with iron oxide, to which has been added a small amount of metallic mercury.
The positive plate consists of a nickel-steel grid to which are secured perforated steel
tubes reinforced by seamless steel springs. These tubes are filled with alternate layers of
nickel hydrate and very thin plate nickel firmly and carefully packed by a loading machine.
82. The Charge and Discharge of the Edison Cell. — The process taking
place in an Edison cell during charge and discharge is as follows :
The first charging of an Edison cell reduces the iron oxide to a metallic iron, while
converting the nickel hydrate to a very high oxide, black in color. On discharge, the
metallic iron goes back to iron oxide and the high nickel oxide goes to a lower oxide, but
not to its original form of green hydrate. On every cycle thereafter the negative charges
to metallic iron and discharges to iron oxide while the positive plate charges to a high
Fig. 87a. — Group of Electric Storage Battery Co.'s Portable
Chloride Storage Cells.
nickel oxide. Current passing in the direction of charge or discharge, decomposes the
potassium hydrate of the electrolyte and the oxidation and reduction of the electrode are
brought about by the action of its elements. An amount of potassium hydrate equal to
that decomposed is always reformed at one of the electrodes by a secondary chemical
reaction,' in consequence there is none of it lost and its density remains constant.
The final result of charging is, therefore, the transference of oxygen from the iron to
the nickel electrodes and that of discharging is the transference back again.
A hydrometer reading of this cell is not required as the specific gravity of the elec-
trolyte does not change with the state of charge or discharge and consequently the only
direct method to measure the state of charge is with an ampere hour meter, the hydrometer
being of no use.
PART VI.
THE RADIO TRANSMITTER
CONDENSERS— OSCILLATION GENERATORS— RADIATION
ELECTRICAL WAVES— DAMPING OF OSCILLATIONS.
OF
83. METHODS OF GENERATING RADIO FREQUENCY CURRENT.
84. THE CONDENSER. 85. CONNECTIONS FOR CONDENSERS.
86. How TO PLACE A CHARGE IN A CONDENSER. 87. ANALYSIS
OF A SPARK DISCHARGE. 88. EFFECT OF RESISTANCE ON OSCIL-
LATIONS. 89. ELECTRICAL RESONANCE. 90. THE OPEN CIR-
CUIT OSCILLATOR. 91. THE LENGTH OF THE ELECTRIC WAVE.
92. THE DETERMINATION OF WAVE LENGTH FROM THE INDUC-
TANCE AND CAPACITY. 93. LOGARITHMIC DECREMENT OF THE
OSCILLATIONS. 94. METHODS OF EXCITING OSCILLATIONS IN
AN AERIAL. 95. THE REACTION OF COUPLED CIRCUITS. 96.
THE STANDARD WAVES OF COMMERCIAL WIRELESS TELEGRAPHY.
97. FUNDAMENTAL CIRCUIT OF A COMPLETE RADIO TRANS-
MITTER. 98. SIMPLE EXPLANATION OF THE CIRCUITS. 99.
NUMERICAL VALUES FOR A STANDARD RADIO SET.
Fig. 88 — Oscillations of Constant Amplitude.
CONSTANT AMPLITUDE
The electric waves for commercial wireless telegraphy are set into motion by
alternating" currents or electrical oscillations at frequencies varying from 25,000
to 1,000,000 cycles per second. We shall confine this chapter to an explanation
of the apparatus for the production of damped electrical oscillations which are
employed almost universally for wireless ship to shore communication.
83. Methods of Generating Radio Frequency Current. — In order to distin-
guish alternating currents of the order of frequency employed in wireless teleg-
raphy from those of. a lower frequency corresponding to audible vibrations,
the following arbitrary terms are in
use; an alternating current of fre-
quency in excess of 10,000 cycles per
second, is termed a current of radio-
frequency; below 10,000 cycles per
second, it is called a current of
audio-frequency.
A current of radio-frequency
may consist of either continuous or
discontinuous oscillations. A group
of oscillations of continuous ampli-
tude are shown in Fig. 88; a group
of discontinuous oscillations appear
in Fig. 89.
Continuous oscillations are gen-
Fig. 89— Oscillations of Decreasing Amplitude. Crated :
AMPLITUDE
THE RADIO TRANSMITTER.
81
(1) By the radio frequency alternator;
(2) By some form of the D. C. arc generator;
(3) By a battery of vacuum tube bulb.
Discontinuous oscillations are generated :
(1) By the charge and discharge of a Leyden jar or battery of condensers.
Electric waves set into motion by alternating- current of constant amplitude
are called continuous or undamped waves and those set into motion by discon-
tinuous oscillations occurring in groups are called discontinuous waves. Electrical
oscillations of decaying amplitude are also called damped oscillations.
Since damped oscillations are generated by the periodic charge and discharge
of some form of condenser, certain fundamental facts concerning the condenser
will now be considered.
84. The Condenser. — The condenser may be defined as a device to store up
electrical energy in electrostatic form and the ability of any material to do this, is
termed its electrostatic capacity or simply capacity.
The most common form of condenser used in wireless
systems is the Leyden jar shown in Fig. 90. A glass jar having
walls about one-eighth of an inch in thickness is coated with
tin-foil to within two inches of the top, both inside and outside,
connection being made to the inner coating by means of a chain
or copper strip. Modern jars are coated with a deposit of
silver or copper by an electrolytic process. Another type of
condenser consists of a flat plate of glass coated with tinfoil
or copper immersed in oil.
Condensers for radio telegraphy may be generally classified
under two headings:
(1) High Potential Condensers;
(2) Low Potential Condensers.
Those in the first category have an insulating medium be-
tween opposed conducting surfaces of glass, micanite, ebony, or
the plates may be sealed in an air-tight chamber pumped to a
pressure of 250 pounds.
Those in the second category have an insulating medium of
paper, thin sheets of hard rubber, or specially impregnated
cloth.
High potential condensers are employed in circuits, where
the pressure is several thousand volts, while low potential con-
densers are generally used in circuits having less than 500
volts, the latter figure being an arbitrary one.
A number of condenser jars or Leyden jars connected together are termed a battery of
condensers.
85. Connections for Condensers. — Condensers may be connected either in
series or in parallel. If connected in
parallel as in Fig. 91 the total capacity ~
is determined by adding together the
individual values, or:
C = C-l + C-2 + C-3.
Thus the jars in Fig. 91 have
combined capacity of .002 -j- .003 +
.004 or .009 microfarad.
A series connection is shown in
the diagram, Fig. 92, where the outer
coating of one jar is connected to the
outer coating of the next, the inner
coating of this jar connected to the
inner coating of the next jar and so on.
If the jars have equal values of capacity, their combined capacity is obtained
Fig. 90 — Simple Copper Plated
Leyden Jar.
Fig. 91 — Condenser Jars in Parallel.
82
PRACTICAL WIRELESS TELEGRAPHY.
by merely dividing the capacity of one jar by the number of jars in the cir-
cuit, but if the jars have unequal values, the formula of reciprocals applies:
C =
1
.ooz
MFD.
1 1
C-l C-2 C-3
Therefore the capacity of the jars
1
of Fig. 92 =
1
1
Fig. 92 — Condenser Jars in Series.
.004
.002 .003
: .00092 microfarads.
86. How to Place a Charge in a Condenser. — The condenser of a radio
transmitter may be charged from two sources:
(1) By the step-up voltage induction coil;
(2) By the alternating current step-up transformer.
The alternating current transformer is almost universally employed in radio sets t®
charge the condenser, because it overcomes the limitations of the magnetic interrupter.
A transformer can convert a practically unlimited amount of power into high voltage
current whereas the induction coil with a magnetic interrupter is limited to about 1 K. W.
A condenser can be given a heavy charge by the apparatus shown in Fig. 93. A high-
voltage A. C. transformer, 10,000 to 30,000 volts, is connected to the terminals of three
condenser jars, and when the current is turned on, a violent discharge takes place at the
gap S-l.
,-
10 VOLT *
AC. «
i
_
T
| {
±
— t-
=c
> li
gj
Fig. 93 — Circuit for Production of Radio Frequency Oscillations.
In the diagram Fig. 93 P is the primary winding of an alternating current transformer
taking in current at the pressure of 110 volts, which is transformed in the secondary wind-
ing S to a pressure of 20,000 volts. C is a battery of condensers and L a radio-frequency coil
consisting of a few turns of rather coarse wire or copper tubing (without an iron core).
S-l is the spark discharge gap, the usual form being two brass or zinc rods about ]/2 inch
or less in diameter.
When current is flowing through the primary winding P, with correct separation of the
spark gap electrodes, a violent spark discharge will take place following each alternation
THE RADIO TRANSMITTER.
83
of the charging current or at tfie points, A, B, C, D, E and F shown. The discharge upon
analysis is found to consist of groups of radio-frequent oscillations which alternate through
the condenser and inductance at an extremely rapid rate per second of time. More clearly,
if the frequency of the charging current is 500 cycles per second (or 1,000 alternations), the
condenser C will be charged 1,000 times per second and 1,000 spark discharges will take place
at the gap S. This will result in the flow of 1,000 groups of radio-frequent oscillations
through the discharge circuit.
Fig. 94 — Complete Cycle of Events in the Discharge of a Condenser.
The term spark frequency is employed to designate the number of spark dis-
charges bridging the gap per second of time. In certain types of radio sets the
spark frequency equals the alternations of the charging current, but in other
types the frequency of the sparks may vary in accordance with the general design
of the apparatus (to be explained in the chapter following).
87. Analysis of a Spark Discharge. — A spark discharge such as that
created by the condenser Fig. 94 consists of a series of cycles of alternating cur-
rent of constantly decreasing amplitude, the frequency of which may be very
great. These are known as damped oscillations, a single group of which are
shown in Fig. 89.
The complete cycle of events in the discharge of a condenser may be summarized as
follows: Referring to the diagrams, Fig. 94-a-b-c-d-e : Just previous to the first discharge
the charge in the condenser takes the form of an electrostatic field which is stored up between
the plates as in Fig. 94a. The strain is such that a spark leaps from the positive electrode to
the negative electrode of the gap, that is the collapse of the electrostatic field causes a current
to flow across the spark gap through the inductance L which sets up a magnetic field around
the coil L and connecting leads as in Fig. 94b. Since all of the electrostatic field is converted
to current, the magnetic lines of force collapse back upon the coil L (and connecting leads),
the induced current resulting therefrom recharging the condenser to the opposite polarity as
in Fig. 94c. Although charged in the opposite sense, a quantity of electricity less than
that of the initial charge is stored between the plates, some of the energy having been expended
by the resistance of the circuit and the production of heat, light and sound. The condenser
now discharges across the spark gap in the direction opposite to that indicated in 94b and the
coil L once more is surrounded by a field (Fig. 94d), but which is opposite in polarity to that
of Fig. 94b. These lines of force collapse and recharge the condenser to the polarity indicated
at the beginning of the cycle in Fig. 94a, but a charge less in quantity is stored between its
plates than at the beginning of discharge.
All this may be summed up by saying that when an isolated charge of elec-
tricity is applied to a condenser, and the plates are connected together by an
external circuit, their charges do not completely neutralize at the first instant of
discharge but, in fact, several alterations of current take place before equilibrium
is restored.
This gradual extraction of energy from the oscillations set up by the condenser is termed
the damping of the oscillations and the decrease in amplitude of the successive cycles can be
expressed in a logarithmic percentage.
In the oscillation circuits of a commercial radio-transmitter from a number of complete)
Footnote: The student should compare the time period of a single cycle in a condenser discharge to that
of a 500 cycle alternator. A complete cycle takes place in the circuit of the latter in of a second but a
v 500
single cycle in a group of oscillations of a condenser discharge may take place in various fractions of a
second varying from — of a second to • of a second.
25,000
2,000,000
84 PRACTICAL WIRELESS TELEGRAPHY.
cycles of current may take place, before the charge originally placed in the condenser is com-
pletely dissipated.
The frequency of the oscillations in a condenser discharge circuit may be verv great, in
1
fact, a single cycle may take place in — — of a second, or, in other words, at the rate of
1,000,000
1,000,000 cycles per second, or at even higher frequencies.
The frequency of the oscillations during the discharge of a condenser varies inversely as
the square root of the product obtained in multiplying the inductance of the circuit in henries
by the capacity in farads, or
N- 1
-2»VLC
If L be converted to centimeters and C to microfarads, the formula becomes:
5,033,000
N =i
VLC
As an example, assume that the condenser C, Fig. 95, has capacity of .001 microfarads and
the coil L inductance of 25,000 centimeters (or 25 microhenries) then the frequency
5,033,000
N := — - n= 1,000,000 cycles per second approximately.
The quotient of this problem does not imply that 1,000,000 cycles of current actually took
place in one second but that during the period of oscillation, the condenser discharged through
the inductance at this rate. It must be remembered that the condenser is being charged by an
alternating current and in the case of the 500 cycle alternator it will be charged 1,000 times;
hence in one second there are a number of idle periods during which the condenser receives no
charge.
The student should not confuse the actual number of oscillations in a circuit such as shown
in Fig. 95 with the frequency of the oscillations. As has just been explained the oscillation
frequency is determined by the dimensions
(000
— 24000 CID5. (inductance and capacity) of the oscillatory
^-^-^— ^— ^ circuit whereas the number of oscillations
per single spark is a function of the total
damping of the circuit. It should be under-
stood that an oscillation circuit like that of
Fig. 95 is charged by an alternating current
always will produce, during discharge,
oscillations of constantly decreasing ampli-
.001 MFD /fi\~ tude or damped oscillations.
A circuit like that of Fig. 95 is
termed a circuit of radio-frequency.
The complete apparatus may be called
an oscillation generator and the suc-
Fig. 95 — Closed Oscillation Circuit. ^ ..
cessive cycles of current are termed
high frequency or radio-frequency electrical oscillations. When this apparatus
is employed to generate oscillations of radio-frequency for the production of
electric waves, the circuit is denoted as the closed oscillatory circuit to distinguish
it from the open or radiating circuit.
88. Effect of Resistance on Oscillations. — If in any given oscillation circuit,
Footnote: If the effective resistance of R of an oscillatory circuit be taken into account, the fo/mula for
i nr R*
frequency becomes N= \[ but in the closed oscillation circuits of a practical radio telegraph
transmitter, the value of R is rather small and is usually ignored.
THE RADIO TRANSMITTER. 85
a certain critical value of resistance is exceeded, the discharge of the condenser unll not be
oscillatory. The relation between the resistance of a circuit and the non-oscillatory condition
is expressed as follows : If the resistance R is greater than 2 \l -— , the circuit is non-oscilla-
tory; if resistance is equal to 2 V — the circuit is just oscillatory. If the resistance is less
than 2 y p— the circuit will he oscillatory and will be suitable for the production of radio-
frequency oscillation.
In this equation R is expressed in ohms, L in henries, and C in farads. The value of
1 \/ — is seen to be the critical resistance to cause a given circuit to be non-oscillatory.
The elements of a closed oscillation circuit in a radio-transmitter are connected together
with very heavy stranded copper wire or copper tubing which, excluding the resistance of the
spark gap and other losses, tends to keep the resistance at a minimum ; in fact, practical oscil-
lation circuits do not have anywhere near the critical value of resistance.
Fig. 96 — Circuit for Demonstrating the Phenomenon of Resonance.
Assuming tV resistance of the oscillation circuit of Fig. 95 to be negligible, the frequency
of the oscillations can be varied over given practical limits by variation of either the capacity
or the inductance. If turns are added at the coil L, the current oscillates through the circuit
at a lower frequency ; but if turns are taken out at L, the frequency of the oscillations in-
creases. In a similar manner, increase of capacity at the condenser C will reduce the fre-
quency of the oscillations and decrease of capacity will increase the frequency of the oscilla-
tions. In a radio transmitter the capacity of the condenser C is a fixed quantity, and there-
fore, the frequency of the oscillations is changed by the variable inductance.
89. Electrical Resonance. — The phenomenon of resonance is very striking
in circuits of radio-frequency. In order that the energy of the oscillations flow-
ing in one circuit may be transferred most effectively by electromagnetic induc-
tion, the two circuits must have the same natural frequency of oscillation. In
the diagram of Fig. 96 two circuits of radio-frequency, L, C, S and L1, C1, A are
magnetically coupled at the coils L and L1. If circuit L, C, S is set into oscilla-
tion and the inductance of L1, C1, A carefully adjusted, a point will be found
where the hot wire ammeter gives a maximum deflection. At all other points on
the inductance L, the hot wire ammeter will show a lower reading. It can be
shown that the adjustment of the second circuit where the deflection of the
ammeter is maximum, is such that the two circuits have substantially the same
period of oscillation or the same natural frequency, and it is under such adjust-
ments only that large values of current can be induced in the circuit L1, C1, A.
86
PRACTICAL WIRELESS TELEGRAPHY.
It was shown in paragraphs 45 and 46 that a much greater current will flow in an alternat-
ing current circuit if it contains inductance and capacity of such value that the reactance of
capacity and the reactance of inductance are equal and opposite. This condition exists in
the circuit L1, C, A of Fig. 96 when the ammeter gives the maximum deflection, e. g., the
reactance of the inductance L1 equals the reactance of the condenser C1 and therefore the flow
of current in circuit L1, C1, is governed by its frictional resistance. The maximum amount of
energy will be obtained under these conditions.
Two or more circuits of radio-frequency are said to be in electrical resonance
when the product of the inductance multiplied by the capacity gives a like figure
in each. Or, stated in another way, two circuits are in resonance when they have
the same oscillation constant. This factor is obtained from the VL C. Circuits
having like oscillation constants will have the same discharge frequency when
set into oscillation, and, therefore, they are in electrical resonance. Applying this
._j
Fig. 97a — Plain Aerial Excitation.
Fig. 97b — Showing Position of Short Wave Condenser and Aerial Tuning Inductance.
Fig. 97c — Illustrating the Effective Capacity of an Aerial.
to the circuit of Fig. 96 we see that no matter how large or how small the values
of L and C, L1 and C1 may be, if V L C = V L1 C1, the circuits are in sub-
stantial resonance.
As an example: If in Fig. 96, L = 25,000 centimeters; C = .001 micro-
farads; L1 = 5,000 centimeters and C1 = .005 microfarads; then L X C -
L1 X C1 (for VL C or VL1 C1 = 5).
90. The Open Circuit Oscillator. — In the closed oscillation circuits of figures
95 and 96, the capacity of the condenser and the inductance of the coil are said
to be concentrated, the static field being stored up mainly between the plates of
the condenser and the magnetic field mainly about the coil.
An open circuit oscillator*, such as shown in Fig. 97a, ma*y have distributed
inductance and capacity or both distributed and concentrated values of inductance
and capacity as in Fig. 97b.
*The capacity of this vertical wire lies in its ability to store up static lines of force and the
inductance lies in its ability to store up magnetic lines of force.
THE RADIO TRANSMITTER.
87
In these diagrams a vertical wire* 100 ft. or more in length extends into
space and is connected to earth at the opposite end. A spark gap is included in
the circuit at S-l. Although the inductance and capacity of this circuit are dis-
tributed throughout its length, it remains a circuit of radio-frequency capable
of being set into oscillation. If the spark gap S-l, Fig. 97a, is connected to a
source of high voltage S such as the secondary winding of a transformer, an
electrostatic field will be stored up in the region about the wire and a discharge
will take place across the spark gap. This discharge will consist of radio-
frequency oscillations like those of closed oscillation circuits with the exception
that a certain amount of the energy will be radiated in the form of electro-
magnetic waves.
As in the closed circuit, the fre-
quency of the antenna oscillations can
be increased or decreased by change
of inductance or capacity, but since the
vertical conductor has fixed dimen-
sions, the oscillation frequency in prac-
tice is changed by artificial means at
the base of the aerial. For example,
in the apparatus of Fig. 97b, the fre-
quency of the oscillations can be re-
duced by increase of inductance at L
or it may be increased by inserting a
condenser at C.
In the diagram of Fig. 97c, the
effective capacity of an antenna is
represented by a condenser in dotted
lines. This in no measure illustrates
\
/ ^- ^— — - W-. -— — •*
\
/ /" ^vlX *
^ \
/ x -T-
\ \
/ X — . ^
V \
/ / T N
\ \
\ \ \
\ii s*' ~~jt~ ^>
\ \ • \
/ , / / • \
/ I I / A \
\ \ \
\ \ \
\ \ \
Fig. 98 — Electrostatic Field About Aerial Previous t<
Spark Discharge.
the true conditions of affairs in the region about a vertical wire, but it may serve
to make the oscillating properties of a vertical conductor more or less self-evident.
An open circuit oscillator in radio-telegraphy is known as an aerial or an
antenna, and it is said to be a radiator of electromagnetic waves. In commercial
practice, aerials may have 2, 4 or 6 wires connected in parallel.
/n r\
"
LENGTH OF
- + +•»• —
R A
_ LENGTH OF
+ "t"
Fig. 99 — Detached Loops of Electrostatic Strain.
The complete process of radiation of electromagnetic waves is a complex subject which
will only be treated in a popular manner here. The vertical wire of Fig. 98 and the earth
may be considered as two sides of a condenser having a certain capacity, and when the spark
gap is connecled to a source of high voltage, electrostatic lines of force will be stored up ii>
the space surrounding the aerial and when the maximum charge has been reached, a discharge
takes place across the spark gap. Immediately the spark discharges, part of the electrostatic
field is converted into current and the remainder into a wave motion.
The wave motion consists of an expanding static field (as shown in Fig. 99) which is
88
PRACTICAL WIRELESS TELEGRAPHY.
accompanied by a magnetic field both being radiated at right angles to each other and to the
direction of propagation. (The magnetic field for a single cycle of current in the oscillator is
shown in Fig. 100). This wave motion is propagated
through space at a velocity of 186,000 miles per second
corresponding to 300,000,000 meters.
At a distance from the aerial system and near to the
earth we may crudely represent the fluxes of this wave
motion by the crossed arrows of Fig. 101, where the
vertical arrows represent the electrostatic field and the
horizontal arrows the magnetic field. If these two fluxes
act upon another vertical conductor (or elevated ca-
pacity) of identical natural frequency of oscillation as
the transmitter aerial, a feeble current will be induced
which can be de-
tected by several
methods. If means
are provided t o
C <^ ^ ^>^>^> I I I I control the energy
of the radiating
station in the form
of the dots and
dashes of the tele-
graph code and if
appropriate d e -
vices are supplied
at the receiving
station whereby
the received en-
ergy can be inter-
preted or made
audible, we then
have a complete
system of wireless
telegraphy.
Fig. 100 — Magnetic Field around an
aerial for three alternations of current.
Fig. 101 — Aerial in Path of Advancing
Electromagnetic Wave.
91. The Length of the Electric Wave. — If we were to determine the length
of a single wave, in a wave motion like that of the diagram Fig. 102, we would
simply measure the physical distance between two points in the successive waves
where the disturbance is at a maximum or a minimum, as from A to B or C to D,
or between any two points of equal disturbance. Similarly the distance between two
points in two successive electric waves
where the electrostatic or the elec-
tromagnetic field is maximum and in
the same direction would be the
wave length of the electromagnetic-
wave. The distance from A to B in
Fig. 99 represents the length of one
complete wave, which can be ex-
pressed in feet or in meters. The
standard zvave lengths of commercial
Fip.
102. — Showing .Veasurement for the Length of
Single Wave.
radio-telegraphy are 300, 450 and 600
meters corresponding approximately to 1,000, 1,500 and 2,000 feet.
The relation between the velocity of electric waves, the length of a single wave and the
number generated per second, can be explained as follows: Assume, for example, that 1,000,-
000 waves pass a given point in a second of time and that each wave is of 300 meters length ;
then the distance through which the first wave has travelled in one second will be equal
to the number of waves multiplied by the length of one wave or 100,000,000 X 300 or
300,000,000 meters. In other words, the distance travelled by the wave motion in one second
is the velocity of the wave. This may be written :
THE 'RADIO TRANSMITTER. 89
Velocity = (Number of waves) X (Length of a single wave), which may also be written:
the velocity of electric waves
Length of a single wave = —
the number of waves
It has been proven by experiment that the velocity of electromagnetic waves is practically
the same as the velocity of light which may be taken as 186,000 miles per second or the
equivalent of 300,000,000 meters. Keeping in mind that a single cycle of current in an open
circuit oscillator sets into motion a single electric wave, the foregoing formula can be written :
300,000,000
Length of one wave = —
frequency of the oscillations
Hence if a vertical conductor oscillates at a frequency of 500,000 cycles per second, the length
300,000,000
of one wave in the resultant wave motion will be — — = 600 meters. -
500,000
If the wave length is expressed by the symbol \ the velocity of electric waves by V and
the frequency of the oscillations by N, the formula may be written :
V
X = —
N
A table of standard wave lengths corresponding to various oscillation frequencies follows :
Wave Length in Meters. Frequency in Cycles per Second.
200 1,500,000
300 1,000,000
450 666,666
600 500,000
1000 300,000
2000 150,000
3000 100,000
6000 50,000
8000 37,500
10000 30,000
92. The Determination of Wave Length from the Inductance and Capacity.
—The length of the wave radiated from an open circuit oscillator can be calculated
directly from knowledge of the effective* inductance and the effective capacity
of the aerial. The formula may be written :
Wave length = 38 X V~L~C~
Where L — the inductance in centimeters ;
And C = the capacity in microfarads.
If an inductance coil is introduced at the base of an aerial, the formula must
be modified to read :
6.2832
Wave length = X 9.5 X V L C
K
Where K = a certain correction factor (see appendix).
The wave length of a straight vertical aerial of the type indicated in Fig. 97a can be
determined approximately from the physical dimensions. The length of the wave radiated
from a grounded vertical oscillator is found to be approximately 4.3 to 4.5 times its length.
Therefore if the vertical wire of Fig. 97a is 100 ft. in length, a single electric wave would have
length of 4.3 X 100 = 430 ft. and since 1 meter = 3.25 feet, the wave length is approximately
132 meters. If the aerial consists of several wires connected in multiple, the factor 4.3 does
not apply owing to the increase in the capacity of the aerial system. However, in the case of
a 4 wire aerial, the wires being spaced about 21/? ft. apart, we may assume the factor of 4.4 to
4.8 which multiplied by the total length of the aerial in feet or meters gives an approximation
of the fundamental wave length.
*The effective capacity is the capacity of the aerial as an element of an oscillation circuit. This
value varies with each change of \.
90
PRACTICAL WIRELESS TELEGRAPHY.
When we speak of the wave length of a closed oscillation circuit reference is made to the
particular frequency at which the circuit oscillates and to the length of a single wave in the
resultant wave motion if the circuit were radiative. Thus if the frequency of a given closed
oscillation circuit is 500,000 cycles per second, it would correspond in the case of an open
circuit oscillator to a wave length of 600 meters. Hence, we would state that the wave length
of the closed oscillation circuit is 600 meters.
The wave length of a closed oscillation circuit may be computed as follows :
Wave length = 59.6 X V~L~C~
Where L = The inductance of the circuit in centimeters ;
And C = The capacity of the condenser in microfarads.
We see from this that if a given closed oscillation circuit had inductance of
10,000 centimeters and capacity of .01 microfarads, the wave length would be
59.6 X V~l66~ = 596 meters.
93. Logarithmic Decrement of the Oscillations. — When electrical oscilla-
tions are created in an antenna or
other circuit by means of condensers
discharges, each electric spark dis-
charge creates a train of oscillations
which die away. The oscillations are
assumed to decay away according to
the law that the ratio of any oscillation
to the one preceding is constant. This
constant ratio is called the damping of
the oscillation and the Naperian loga-
rithm of the ratio of one oscillation
to the preceding one is .called the
logarithmic decrement.
Fig. 103— Highly Damped Oscillations.
Thus in the group of oscillations of Fig. 103, the maximum amplitudes of
successive alternations are represented by A1, A2, A3, A4, etc., and
A^=JA8 - A*.
A3 A5 A7 ' e
In terms of logarithms we may write
where e = base of the Naperian system of logarithms ;
$ = a constant termed the logarithmic decrement.
By transposition
3 -1 or A'
If we' assume that the oscillations in a circuit are extinguished when the ampli-
tude of the last oscillation is .01 of the initial oscillation, the complete number of
oscillations (M) in a spark discharge can be computed as follows:
log
M=-
A*
If we denote the last oscillation by Ax then — = 100, and since the Logarithm of 100 = 4.605
then
THE RADIO TRANSMITTER.
91
Hence in a group of oscillations
Where 5 = 0.1
4.605 + 0.1
M =
0.1
= 47 complete oscillations.
The tuning qualities of a train of electric waves from any given transmitting station depend
greatly upon the decrement of the oscillations and, therefore, the determination of the quantity
is an important measurement. It is found
-Feebly Damped Oscillations. by experiment that a transmitter having
less than 24 complete oscillations in the
antenna circuit per single spark discharge,
possesses undesirable tuning qualities and
will interfere with the operation of other
radio stations not tuned to the same wave
length.
A group of 24 complete oscillations
corresponds to a decrement of 0.2 for a
complete oscillation which is the arbitrary
figure enforced by U. S. Statutes. This
means that if the oscillations in a
given antenna circuit have a decrement
A*
of 0.2, the logarithm of the ratio of —
A3
will be 0.2. (The number corresponding
to the logarithm 0.2 is 1.2, hence the ratio
A1
of — must be 1.2 for a decrement of 0.2.)
AS
A group of oscillations of feeble
damping are shown in Fig. 104; a
highly damped group in Fig. 105.
If the conditions of damping de-
picted in Fig. 104 apply to an open
circuit oscillator at any given radio station, the energy of the radiated wave is
largely confined to a single frequency and the effect at the receiving apparatus is
termed in operators' language "sharp tuning" meaning that very careful adjust-
ment is required at the receiving station to place the receiving apparatus in
resonance with the distant transmitter, i. e., the transmitting apparatus is said
to be "sharply tuned." But with the conditions of Fig. 105 the transmitter is
" broadly tuned" and the radiated wave said to have "excessive damping"
These trade expressions are more or less comparative because the damping of
the receiver is not taken into account. However, the terms may be applied in a
practical way. In any given transmitter, oscillations of great amplitude or
strength but of feeble damping are really desired, but in certain types of ap-
paratus the conditions favorable to one offset the conditions favorable to the
other; hence we are required to effect a compromise.
The exact meaning of the logarithmic decrement of the oscillations in radio-telegraphy
may be better understood by considering the oscillating movements of a pendulum in me-
chanics. Suppose for example a plumb bob is attached to the end of a string and suspended
freely as in Fig. 105a ; drawn to one side and released, the bob will vibrate to and fro until
the oscillation is completely damped out. If a piece of cardboard, for instance, were attached
to the string, the oscillations of the pendulum would come to a stop in a much shorter period,
e. g., they would be said to be highly damped. This corresponds to the damping of the oscil-
lations in a radio oscillation circuit having considerable resistance.
Now the time period of one complete oscillation of the pendulum can be obtained by
counting the oscillations for one minute and dividing their number by 60. Hence if 60 corn-
Fig. 105 — Oscillations with Excessive Damping.
92
PRACTICAL WIRELESS TELEGRAPHY.
plete oscillations took place per minute, the time period of one oscillation would be one
second. This could he easily arranged if the string of the pendulum had a certain length and
the bob a certain weight.
Assume that the bob oscillated in front of a scale calibrated in inches as in Fig. 105a and
that at the beginning of the first oscillation
it was drawn from the zero position out-
ward to a distance of 15 inches. On ac-
count of wind friction, at the end of one-
half oscillation the bob would not have
travelled 15 inches from the zero position.
Under suitable conditions it would move
outward, let us say, 14.2 inches and in the
return swing, its movement would be still
less, say 13.5 inches. That is, the swing of
the second oscillation would be \l/2 inches
less than the initial oscillation.
If we observe the length of the succes-
sive swings and plot the results as in Fig.
104, we would obtain a group of decaying
oscillations which would bear the following
ratio to one another. If the horizontal axis
A, B is divided into seconds, and the ampli-
tude of the right and left swings of the
pendulum shown by -the notations on the
vertical axis, (0 to 15, in either direction)
then the amplitude at the termination of a
complete period or at any partial period of
oscillation will be as follows : at the end
Fig. 105a — Pendulum for Illustrating Damping.
of the first half period, the amplitude of the oscillation will be 14.2; at the end of a complete
period, 13.5. After the pendulum has been in oscillation for \y2 seconds, the amplitude will
be 12.8 and at the end of two seconds, 12.1 and so on.
It is to be especially noted that the ratio of the amplitude of the successive oscillations is
constant, e. g., 15/13.5 = 1.11; 13.5/12.1 = 1.11, and so on. This ratio will be constant to the
end of the swings of the pendulum because it is a law of all mechanical oscillating motions,
that the oscillations will die away at such rates that the ratio of successive amplitudes remains
constant. This is the condition assumed to exist in the spark discharge circuits of radio
transmitters.
It should now be clear that if the friction to the oscillation of the pendulum were increased
by attaching a cardboard damper to the pendulum, the swings would die out more rapidly and
the ratio of the successive amplitudes would take a higher figure. The damping of the
oscillations would thus be increased. We see from this that slow damping corresponds to
a great number of swings of the pendulum whereas rapid damping corresponds to a small
number of swings of the pendulum.
Now the ratio of the amplitude two successive oscillations is called the damping factor
and the logarithm of this ratio is called the logarithmic decrement. In the problem cited the
ratio is 1.11 and if reference is made to any table of Naperian logarithms, the logarithm of
1.11 will be found to be approximately 0.10. Similarly if the ratio were 1.22, the logarithmic
decrement would be 0.2, the limit allowed by law.
The decrement of the oscillations flowing in the aerial of a modern radio-transmitter is
4.605 + .05
frequently .05 per complete cycle, hence for each spark there will be or 92 complete
.05
oscillations.
It is now apparent that the feebler the decrement, the greater will be the number of
oscillations per spark and provided their amplitude does not fall too much, the stronger will
be the current induced in the receiving aerial per spark of the transmitter. This combined
with the favorable tuning qualities of a feebly damped transmitter brings about very desirable
conditions.
THE RADIO TRANSMITTER.
93
The damping of a circuit of a radio-frequency depends upon the effective capacity, in-
ductance and resistance of that circuit. These quantities are related in the following manner :
5 = 1.57 X R1 X t/£-
Where R1 = High frequency resistance in ohms,
C — Capacity in farads,
L = Inductance in henries,
8 = Decrement per semi-oscillation.
C
The ratio of — changes the values of R1 but we may state generally that increase of L or
L
decrease of C will reduce the damping of the oscillations, e. g., decrease the logarithmic
decrement.
Assume a circuit of .ol microfarads capacity, inductance of 10,000 centimeters and resistance
of 3 ohms, then
5 = 1.57 X 3
f .00000001
x V
= 0.148
.00001
Practical measurement of the logarithmic decrement will he described in Part XI.
94. Methods of Exciting Oscillations in an Aerial. — The antenna circuit
can be set into oscillation in ordinary spark telegraphy in several different ways
as follows :
(1) By direct excitation (plain aerial connection);
(2) By inductive coupling to a closed oscillation circuit;
(3) By conductive coupling to a closed oscillation circuit;
(4) By capacitive coupling to a closed oscillation circuit;
Direct excitation of the aerial has been shown in Fig. 97a, where the spark
gap is connected directly in series with the antenna circuit. The winding S is
the secondary of an induction coil wherein the pressure of the current is several
thousand volts. This coil is generally fitted with a magnetic interrupter and
energized by a 15 to 30 volt storage battery.
The advantage of this method of excit-
ing oscillations in the aerial lies in the sim-
plicity of the connections but there are sev-
eral objections to its use. The principal
objection is the fact that the oscillations
are rapidly damped out and the waves
radiated from the aerial will interfere with
the reception of signals at other stations
even when not tuned to the frequency of
this transmitter. The second disadvantage
is that the insulation of the aerial is sub-
jected to an abnormal strain caused by the
high voltage necessary and by the low fre-
quency current of the induction coil being
superposed on the radio-frequent oscilla-
tions.
The oscillations in the antenna circuit of
the plain aerial transmitter will be damped
out less rapidly if fair amounts of induct-
ance are inserted at the base as at L, Fig.
97b. Under these conditions, the decrement
of the oscillations may compare favorably
with modern methods of excitation.
Indirect methods of antenna excitation are shown in Figures 106, 107 and 108. The
principal advantage of these methods of coupling lies in the fact that the closed circuit con-
denser acts as a reservoir of energy and since the capacity of the condenser in the closed
oscillation circuit is generally several times that of the capacity of the aerial, it permits the
closed circuit to use large amounts of power for the same wave length, spark frequency and
•©©•
\ 106- Inductively Coupled Transmitter.
94
PRACTICAL WIRELESS TELEGRAPHY.
voltage which results in the production of more powerful oscillation. Then by proper adjust-
ment of coupling, these oscillations may be transferred to the antenna systems at a certain
rate and radiated in the form of electro-magnetic waves.
Inductive coupling of the open and closed oscillation circuits is shown in the
diagram. Fig. 106. The spark gap S is now placed in the closed oscillation
circuit, the oscillations generated in the latter are transferred to the antenna
through the oscillation transformer, L, L-l.
When the condenser discharges through L, the lines of force cut through L1,
setting up in the aerial circuit oscillations of similar frequency provided the aerial
circuit is carefully tuned to the closed circuit. Winding L is seen to serve the
double purpose of governing the frequency of the oscillations in the condenser
circuit and transferring them by magnetic induction to the aerial circuit.
If L and L1 are closely coupled, the oscillations in the aerial system will be damped out
rapidly due to a part of the energy being retransferred back to the spark circuit, but if L
and L1 are loosely coupled (drawn apart) the oscillations in the aerial circuit will be damped
out less rapidly. We see from this that the
ALRIAL \ I / tuning1 qualities of the transmitter are
\ / largely controlled by the coupling of the
^ oscillation transformer. It is usual to ad-
just the coupling to a degree that will give
oscillations of. fairly feeble damping pro-
vided the flow of the current in the an-
tenna circuit is not seriously reduced
thereby.
Conductive coupling of the closed
and open oscillation circuits is shown
in Fig. 107, where an auto transform-
er is employed to transfer the oscilla-
tions to the antenna. In this diagram
the turns from A to B constitute the
primary winding and the turns from
C to D, the secondary winding. When
condensers C-l, C-2, discharge
through winding P, an alternating
magnetic field threads through S,
which follows the primary current.
Oscillations of radio-frequency are thus induced in the secondary circuits. The
advantage of this method of coupling lies in the simplicity afforded by the use
of a single helix for transforming the oscillations. The inductively coupled sys-
tem, on the other hand, requires a primary and secondary helix with the necessary
mechanical arrangements for adjust-
ment of the coupling. There is little
difference in the degree of efficiency
obtained by these two methods of
coupling; but the coupling between
the closed and open oscillation
circuits can be more easily adjusted
by the inductive transformer than
by the conductive transformer. If
the earth connection to the helix
in Fig. 107 is fitted with a contact
clip, the turns included from C to D
can be placed at a distance from the
turns in use between A and B and in
this manner the coupling between the F:g. ios— One Method of Capacitive Coupling.
Fig. 107 — Conductively Coupled Transmitter.
THE RADIO TRANSMITTER.
95
two circuits can be closely adjusted, but, of course, with greater difficulty than
in the inductive system.
In the capacitive coupling shown in Fig. 108, a condenser C-2 is connected
in series with the aerial system and is also placed between the plates of the
condenser C-l, which is a part of the closed oscillation circuit. Part of the elec-
trostatic field of C-l is transferred to C-2 and accordingly oscillations will flow
in the aerial circuit.*
The majority of radio stations employ the inductive method of coupling.
95. The Reaction of Coupled Circuits. — We might expect that when the
open and closed oscillation circuits of a radio-telegraph transmitter are adjusted
independently to a frequency corresponding to a wave length of 600 meters and
afterwards the circuits are coupled for the transference of energy, the radiated
wave would be of the same length but this may not be the case. Under certain
conditions of coupling, oscillations of two frequencies occur in the antenna circuit.
For example, if the closed and open circuits are set for the wave of 600 meters, we may find
(by means of a wavemeter) two waves being radiated from the aerial, one 630 meters in
length and the other 570 meters in length, corresponding to two distinct frequencies of oscilla-
tion. These two frequencies are caused by the reaction of the magnetic field of the open
circuit upon the closed circuit, and vice versa, that is, the oscillations flowing to and fro
through the primary circuits induce currents in the secondary circuit and the magnetic field
of the secondary currents tends to react
and induce currents in the primary. PRIM-
This interchange of energy goes on un-
til the current in the primary can no
longer bridge the spark gap when the
process stops. This interlinkage of the
lines of force of the two windings causes
the effective self-induction of the an-
tenna coil either to increase or decrease
according to which of the two circuits
is driving the other, and results in the
production of two sets of oscillations.
The resulting oscillations of coupled
circuits may be shown by the dia-
gram of Fig. 109, where two groups of
oscillations in the closed and open cir-
cuits are represented. It will be noted
that the oscillations in the closed cir-
cuit have maximum amplitude when
those in the open circuit have minimum
amplitude, and vice versa. In the sense of a second of time the two sets of oscillations take
place simultaneously, but in the sense of a fraction of a second they do not reach their
maximum amplitude simultaneously.
When the antenna oscillates at two distinct frequencies, two waves of different length are
set into motion. This is an undesirable condition, (1) because the receiving apparatus gen-
erally can be tuned only to one of the radiated waves, the energy of the other being lost;
(2) a needless amount of interference is caused thereby to the operation of other radio
stations.
The true coefficient of coupling between two circuits of this character is determined
by the following formula:
M
Fig. 109 — Showing Oscillations in Primary and Secondary
of Coupled Transmitter.
where L1 and L9 — self-inductance of the primary and secondary circuits respectively,
M = coefficient of coupling.
It is the custom to determine the coupling from actual measurement of the radiated
waves, or
*This is coupling by electrostatic induction. Direct or conductive electrostatic induction may also
be used.
96
PRACTICAL WIRELESS TELEGRAPHY.
X22 — X2i
X'j -f X2i
\Vhere \* — longer wave,
Xi — shorter wave.
Also if Xs equals the wave length to which the primary and secondary circuits are ad-
justed independently, then
X2 = Xs V~~l + K
Xi - X3 V 1 — K
In other words, if the value of the coupling K is known, the two wave lengths can
be calculated before actual measurement.
When the primary winding of the oscillation transformer is placed close to the second-
ary winding, perhaps partially telescoped into it, the set is said to have "tight coupling" or
"close coupling," but when these two windings are drawn apart the coupling is said to be
"loose."
Now if oscillations of two frequencies flow in an aerial system, and afterward the
coupling is gradually reduced, the two sets of oscillations gradually merge into oscillations
of a single frequency and generally with this adjustment, the radiated wave is feebly
damped or of low decrement ; i. c., it has the damping of the antenna circuit.
The student should note this carefully: With the plain spark discharger in the closed
circuit, "close coupling" of the primary and secondary windings generally causes a "broad
•wave" to be radiated from the aerial system, while "loose coupling" results in the radiation
of a "sharp wave." The terms are, of course, merely relative. (See Appendix, Section G.)
o .
Q I
T-2
FOR 300 METER5 OPEN
5-1 AND REDUCE INDUCTANCE
AT T-i T-2 \
Fig. 110 — Diagram Showing Changes Necessary to shift from 600 meter to 300 meter Wave.
96. The Standard Waves of Commercial Wireless Telegraphy.— The rules
of the International Radio-Telegraphic Convention require the use of tivo stand-
ard waves for the dispatch of commercial wireless traffic, namely 300 and 600
meters. Either of these waves must be employed for calling another station but
THE RADIO TRANSMITTER. 97
after communication is established, waves of any length between 300 and 600
meters may be used. The rules also specify that by special license vessels may
employ waves in excess of 1600 meters.
For ordinary marine traffic, naval stations of the United States employ waves
varying in length from 600 to 1600 meters. High power naval and commercial
stations use waves varying from 1600 meters to 10,000 meters. The United
States regulations limit amateur stations to the use of a 200 meter wave with
power input of 1 K. W. If the amateur station is located within five miles of a
naval station their sets are limited to an input of ^2 K. W.
The standard marine radio sets of the Marconi Wireless Telegraph Company
of America vary in power from y$ K. W. to 2 K. W. and are designed for three
waves of 300, 450 and 600 meters length.
The average ship's aerial in the Marconi service has a fundamental wave length of 325
meters, capacity of approximately of .'001 microfarads and inductance of 70,000 centimeters. In
order that the standard waves of 300 and 600 meters may be radiated, an extra inductance
must be included at the base for the 600 meter wave and a condenser must be connected in
series for the 300 meter wave. This coil and condenser are called: (1) the aerial tuning
inductance; (2) the short wave condenser. The aerial tuning inductance various from
20,000 to 80,000 centimeters inductance and the short wave condenser usually is of fixed
capacity, approximately .0005 microfarads. The position occupied by these devices in the
antenna circuit is shown in Fig. 110. The condenser is shunted by a switch S-l which is
closed for the 600 meter wave. The tuning inductance L-3 is fitted with a plug contact
permitting one turn or a fraction of a turn to be inserted in the circuit at A1.
The method of shifting from one standard wave to the other in a commercial
set is shown in Fig. 1 10. Assume the open and closed circuits to be set for the
600 meter wave : Then if the circuits are to be adjusted for 300 meters, the
following procedure is involved:
(1) The variable contact T-l at the primary winding of the oscillation trans-
former is set at a lesser value of inductance (as indicated by the dotted
lines) ;
(2) Similarly the variable contact of the aerial tuning inductance L-3;
(3) The switch S-l shunting the short wave condenser is opened.
If the condenser of the closed circuit exceeds .015 microfarads capacity, its capacity must
be reduced for the 300 meter wave, to say, .006 microfarads.
When a condenser is connected in series with an open circuit oscillator, the total
capacity is affected just as it is when two ordinary condensers are connected in series,
i. e., the capacity is reduced and the resulting value will be less than the capacity of the
smallest condenser in the circuit. We have already shown that the wave length of an
open circuit oscillator = 38 V LC ; hence a decrease of the value of C will decrease the
length of the radiated wave.
We may then write for the open circuit oscillator,
-L CC-
c + c3
where C3 — capacity of the short wave condenser.
When an extra coil of inductance is inserted at the base of an aerial the formula becomes
6.28
X = X 9.5 V LC
K
Where K = a certain correction factor, the ratio of the inductance of the coil to the
inductance of the aerial ;
L = total effective inductance of the aerial in centimeters ;
C = capacity of the aerial in microfarads.
If very large values of concentrated inductance are inserted at the base of the aerial,
the correction factor may for all practical purposes be ignored.
97. Fundamental Circuit of a Complete Radio Transmitter. — We have
shown how alternating current can be obtained from a generator and how it can
be raised to a pressure of several thousand volts by a step-up transformer. It
has been explained that this current of high pressure can be stored up temporarily
98
PRACTICAL WIRELESS TELEGRAPHY
THE RADIO TRANSMITTER. 99
in a condenser and discharged through the closed circuit in the form of radio-
frequent oscillations, and that these oscillations can be transferred to an aerial
circuit, where a part of their energy is radiated in the form of an electromagnetic
wave. We see, then, that the principal parts of a radio-transmitter are :
(1) The alternating current generator;
(2) The alternating current step-up transformer;
(3) The condenser;
(4) The oscillation transformer;
(5) The aerial or antenna;
(6) The short wave condenser;
(7) The aerial tuning inductance;
(8) The transmitting key.
(9) The spark gap.
The student should now focus his attention on the diagram of Fig. Ill where
direct current enters the motor at the left of the drawing but eventually at the
extreme right, an alternating current of radio-frequency flows in the antenna
circuit.
A complete transmitting set consists of the following apparatus:
(1) A motor generator to convert direct current to alternating current.
(2) A starting box to regulate the flow of current through the motor armature
during the starting period.
(3) Field rheostats to regulate the frequency and the voltage of the generator.
(4) A step-up transformer to raise the voltage of the alternating current to a
value in excess of 10,000 volts.
(5) An ammeter to measure the current flowing through the transformer.
(6) A voltmeter to measure the voltage at the terminals of the alternator.
(7) A wattmeter to measure the power input to the transformer.
(8) A reactance regulator to regulate the flow of current through the primary
winding of the transformer.
(9) A telegraph key to permit the current to be interrupted in the form of the
dots and dashes of the Morse code.
(10) A battery of condensers for the production of radio-frequent oscillations.
(11) A spark discharge gap to discharge the energy stored up in the condenser.
(12) An oscillation transformer to transfer current at radio frequencies from the
condenser circuit to the aerial circuit.
(13) An aerial ammeter to determine conditions of resonance between the con-
denser circuit and the aerial circuit.
(14) A short wave condenser to decrease the time period of oscillation of the
antenna circuit.
(15) An aerial tuning inductance to increase the time period of oscillation of
the antenna circuit.
(16) An aerial change-over switch to shift the aerial alternately from the trans-
mitting apparatus to the receiving apparatus.
(17) An aerial to radiate energy in the form of electromagnetic waves.
98. Simple Explanation of the Circuits. — A simple explanation of the
functioning of this apparatus follows: Direct current, at pressure of 110 volts,
enters the motor armature through the starting box and sets it into rotation. The
alternator in turn generates alternating current at pressures varying from 110 to
500 volts according to the design of the machine.
When the telegraph key is closed, current flows from the generator armature
through the primary winding of the transformer setting up magnetic lines of
force which intersect or cut through the secondary winding inducing therein a
current at pressures varying from 10,000 volts to 25,000 volts.
Now the voltage and the frequency of the alternating current can be adjusted
(by the generator Held rheostat and the motor field rheostat. For example, if re-
sistance be added at the motor field rheostat, the motor will increase its speed and,
accordingly, the frequency of the generator will be increased. This will also tend
to increase the voltage of the generator. If resistance be added at the generator
100 PRACTICAL WIRELESS TELEGRAPHY.
field rheostat, the voltage of the generator armature will be reduced and con-
versely if the resistance of this rheostat is decreased, the voltage of the generator
will increase.
The terminals of the secondary winding of the high voltage transformer are
connected to the terminals of a battery of condensers where the energy is stored
up temporarily in the form of electrostatic lines of force. When the limit of
charge for each alternation of charging current has been reached, the condenser
will discharge across the spark gap through the primary winding of the oscillation
transformer, the discharge consisting of a number of radio-frequent oscillations.
The frequency of the oscillations will decrease if inductance is added at the
primary winding or increase if the inductance be reduced. An increase or de-
crease of the capacity of the condenser affects the frequency in the same manner,
e. g., a reduction of capacity will increase the frequency of the oscillations while
an increase of capacity will reduce the frequency of the oscillations.
The oscillations flowing in the closed circuit are transferred to the aerial cir-
cuit through the oscillation transformer and a portion of the energy is radiated
from the antenna in the form of electromagnetic waves. In a simple single wire
aerial system, the wave length of this wave motion will be approximately 4.3
times the linear length of the oscillator. The length of the radiated wave in
fact varies inversely as the frequency of the oscillation. The higher frequencies
such as 500,000 and 1,000,000 cycles per second correspond to the shorter waves
such as 600 meters and 300 meters respectively, while lower frequencies of oscil-
lation from 30,000 to 100,000, for example, correspond to the longer waves from
10,000 meters down to 3,000 meters.
If a receiving aerial be erected at a distant station and its natural time period
of oscillation adjusted to the frequency of the oscillations flowing in the trans-
mitter aerial, feeble currents will be induced in it which by appropriate devices
may be heard in the receiving telephone. More clearly, the fluxes of the advancing
wave will induce currents in the receiving aerial having substantially the fre-
quency of the oscillations in the transmitting aerial. By appropriate devices
within the station, these currents can be translated into the language of the sender.
99. Numerical Values for a Standard Radio Set. — In order to familiarize
students with the power consumption, the capacity and inductance of the various elements
in a standard transmitting set, the following data is presented. The motor of the
2 K. W. 500 cycle panel transmitting set takes 4.3 H. P., the generator delivers 2 K. W.
Current enters the motor armature at 110 volts D. C., but the voltage developed at the
generator armature is approximately 380 volts on open circuit and approximately 120
volts when the transmitting key is depressed. The frequency of the generator is 500
cycles (this frequency is now standard).
The transformer is of the closed core type; the secondary potential is 14.500 volts.
The capacity of the condenser for the 450 and 600 meter waves is .012 microfarads, but for
the 300 meter wave it is reduced to .006 microfarads.
The primary winding of the oscillation transformer has maximum inductance of ap-
proximately 10,000 centimeters correspondingly lesser values being used for the shorter
waves. The secondary winding has approximately 30,000 centimeters while the two aerial
tuning inductance coils have combined inductance of about 80,000 centimeters. The aerial
ammeter has range 0-25 amperes, the wattmeter, 0-3 kilowatts.
For the standard }/2 K. W. set the motor is rated at 1 H. P., the generator at ^ K. W.
The voltage at the transformer is about 15,000 volts and the capacity of the closed circuit
condenser .004 microfarads. The inductance of the primary at the wave of 600 meters is
approximately 25,000 centimeters. Lesser values are, of course, employed for the 300 and
450 meter waves. The secondary inductance would, of course, be the same as with the
2 K. W. set.
PART VII.
APPLIANCES FOR A RADIO TRANSMITTER
SPARK DISCHARGERS — OSCILLATION TRANSFORMERS — CON-
DENSERS— TRANSFORMERS.
100. IN GENERAL. 101. SPARK DISCHARGERS FOR RADIO TELEG-
RAPHY. 102. ADJUSTMENT OF THE SPARK NOTE. 103. OSCIL-
LATION TRANSFORMERS. 104. AERIAL TUNING INDUCTANCE.
105. THE SHORT WAVE CONDENSER. 106. HIGH POTENTIAL
CONDENSERS. 107. HIGH FREQUENCY "CHOKING" COILS. 108.
HIGH VOLTAGE TRANSFORMERS. 109. REACTANCE REGULATORS.
110. AERIAL CHANGEOVER SWITCH. 111. TRANSMITTING KEYS.
100. In General. — Although the apparatus of the radio transmitter has
been described and discussed in a fundamental way, certain important parts of
the complete set will require more detailed treatment. Principal among these
are the various types of spark gaps, condensers, oscillation transformers, sig-
nalling keys, etc., each of which may take one of several designs or may differ
in their mode of functioning.
101. Spark Dischargers for Radio-Telegraphy. — The functions of the spark
gap in a radio-transmitter arc: (1) to keep the closed oscillation circuit idle until the con-
denser is fully charged; (2) to discharge the energy stored up in the condenser in the form
of radio-frequent oscillations; (3) to
quench the spark, i. e., to restore the gap
to its non-conducting state, when the
energy has once been transferred to the
antenna.
The ideal gap would be one of in-
finite resistance during the charging
period of the condenser but of zero
Fig. ii2-Simpie Spark Discharger. resistance during discharge-a con-
dition partially realized in the rotary gap but not completely fulfilled.
The transmitting sets of the Marconi Company employ four general types of
spark dischargers as listed below :
(1) Plain spark discharger;
(2) Non-synchronous rotary discharger;
(3) Synchronous rotary discharger;
(4) Quenched spark or multiple plate discharger.
(a) In its most common form the plain spark discharger is composed of two
brass, zinc, or copper rods about l/4 or ^ inch in diameter slightly rounded at the
discharge tips and mounted on an insulated base as in Fig. 112, appropriate
means being supplied whereby the length of the gap may be carefully and closely
regulated. By careful adjustment of the condenser capacity, the voltage of the
generator, and the length of the gap, a single spark discharge for each alternation
of the charging current can frequently be obtained, but it is somewhat difficult to
NOTE. The student should understand thoroughly that a spark gap is not required in order that
the condenser discharge may generate high frequency oscillations, but it may be regarded as a necessary
evil. It is self evident that if the spark gap is closed during the charging period of the condenser the
transformer is placed on short circuit.
102
, PRACTICAL WIRELESS TELEGRAPHY.
maintain this state' of adjustment; ill fact, in the majority of cases, multiple dis-
charges are fow^d/ ,"* f.4:
The chief difficulty With the plain '• gap is the tendency to form an arc with consequent
impurity of the oscillation. Various methods have been devised to prevent the gap arcing
such as the use of several gaps in series, or the applying of an air blast either at right
angles to the discharger or through hollow electrodes to the center of the spark discharge.
The latter method is particularly successful for not only is arcing prevented but a very-
clear spark note is obtained as well. Gaps of this construction are generally used in
transmitting sets employing 60 cycle current transformers or induction coils as a source
of high voltage current. (See Section G, Appendix.)
(b) The non-synchronous rotary spark discharger generally consists of a
circular disc of metal or some insulating material fitted with 8 or 10 metal spark-
ing points equally spaced about the circumference, the disc being mounted on the
shaft of a direct current motor with a speed controlling rheostat connected in
series. The disc revolves between two stationary spark electrodes which can be
carefully regulated in respect to the
revolving electrodes. When the two
stationary electrodes are connected in
series with the closed oscillation cir-
cuit of a transmitter, the spark will
discharge whenever an electrode of
the disc comes opposite the station-
ary electrodes and the pitch of the
note will vary as the speed of the
motor.
The non-synchronous rotary dis-
charger is usually fitted to 60
cycle alternating current transmitting
sets, to produce a spark discharge of
musical pitch, but it may be employed
with alternating current transmitters
of any frequency as well.
The construction of the non-synchronous gap is shown in the drawing, Fig. 113, where
an insulated disc D is mounted on the shaft of the motor M. Equally spaced about the
periphery are the spark electrodes, E, E, which extend through the disc. Two stationary
electrodes, D1, D1, are mounted on a base
and are connected to the condenser and
inductance as shown. At the moment one
of the electrodes on the disc comes be-
tween the stationary electrodes, the spark
will discharge and owing to the equal
spacing of the spark points, the spark note
partakes of a musical pitch. Experiments
with this gap indicate that the most ef-
fective results are obtained (with 60 cycle
current) when the disc is driven at a
speed that will give from 200 to 300 spark
discharges per second. The discs are fitted
with the correct number of spark elec-
trodes to give a spark of this frequency
when driven by a motor at speeds varying
from 1,800 to 2,400 revolutions per minute.
A modified type of the non-synchron-
ous gap is shown in Fig. 114 where ten
stationary sparking points are mounted on
two brass sectors. A light contact arm,
A, B, carrying two spark discharge points
is attached to the shaft of a high speed
mi- j r .1 • i . . Fig 114 — Another Type of Non-synchronous Dis-
motor. The advantage of this design is charger.
Fig. 113 — Non-synchronous Rotary Discharger.
ROTOR
STATIONARY
ELECTRONS
MOTOR
APPLIANCES FOR A RADIO TRANSMITTER. 103
that the spark discharge shifts rapidly from one set of stationary electrodes to the other
thereby preventing the discharge points from overheating. Other modified types of this
discharger are in use but they operate on the same fundamental principle.
The principal advantage of the non-synchronous discharger is that it produces a
musical spark tone from a source of low frequency alternating current. As will be seen
from the diagram of Fig. 115, although the condenser is discharged at a uniform rate, suc-
cessive discharges are not of constant amplitude. In Fig. 115 the successive maximum
amplitudes of the charging 'current are indicated at points a, b, c, d, e, f, g, etc., and the
instant during the cycle at which the
A C J[ £ ^ spark discharges by the mark X. It is
easily seen that the spark frequency is
very much greater than the frequency
of the charging current, but the suc-
cessive spark discharges are not of
constant power; but since they are
timed uniformly, a semi-musical note
composed of fundamental tones coupled
with a number of overtones is pro-
Fig. 115 — Showing the Spark Discharge is Superposed duced, having a pitch far more pleasing
on Charging Current. to thfi eaf than that obtained by the
plain discharger. By very careful adjustment of the speed of the rotor, a non-synchronous
gap can be made to discharge the condenser at points of equal amplitude during successive
alternations of the charging current. This results in a more uniform spark note than that
obtained by ordinary adjustments.
(c) For several well defined reasons the synchronous rotary spark discharger
has found almost universal favor. Contrary to the non-synchronous type, the disc
is mounted on the shaft of the alternating current generator to permit the dis-
charge of the condenser to be accurately timed with the alternations of the charg-
ing current.
The disc of the synchronous discharger may be either of metal or of some
insulating material that will withstand the peripheral strain but for mechanical
reasons, the metal disc is preferred. This is firmly keyed to the generator shaft
but not necessarily insulated* therefrom. The disc always will have discharge
electrodes of the same number as the field poles of the generator, and if the sta-
tionary electrodes are arranged so that they can be shifted through a small arc,
then by careful adjustment a high pitched "screeching" spark note will be secured.
A note of this characteristic is particularly desirable for copying signals through
the interference of static discharges at the receiver; particularly if the frequency
of the charging current is 500 cycles per second.
In event that the frequency of the charging current is 500 cycles, the condenser
will be charged and discharged 1,000 times per second, and the resultant spark
note will have a musical pitch corresponding thereto.
The construction of the disc discharger supplied with the 2 K. W. 500 cycle sets of the
Marconi Company is shown in Fig. 116, where a heavy steel disc carrying 30 copper spark
electrodes is firmly keyed to the motor generator shaft. The disc is enclosed in a steel
muffling drum which also acts as a support for the two stationary electrodes A, B, which
are thoroughly insulted therefrom. In addition, this drum is designed so that it can be
shifted through an arc of approximately 25° by the adjusting rod R. This adjustment
permits the most favorable sparking point to be located and results in synchronous dis-
charges, giving a clear, musical spark note.
Not only must the correct position of the stationary electrodes be found for
successful working, but they must be adjusted to give the shortest possible dis-
charge gap without the electrodes actually touching. In the Marconi gap, the
stationary electrodes can be lowered .003 of an inch at a time, and the electrodes
locked in position to prevent actual contact with the revolving disc.
The muffling drum is thoroughly ventilated by a set of air scuppers cast on the
disc which supply a uniform blast of air for cooling the quenched gap of the
Marconi panel sets as well.
*The disc of the rotary gap, in the 2 K. W. 500 cycle set of the Marconi Company is connected
to earth.
104
PRACTICAL WIRELESS TELEGRAPHY.
The necessity for mounting the disc discharger on the shaft of the alternator will be
at once apparent for if the disc were mounted on an independent motor, any variation in the
line voltage would cause the "coming together of the electrodes" and the alternations of
the charging current to fall out of step, but when the disc is mounted on the shaft any
reduction of the frequency of the charging current will be immediately compensated for
by the simultaneous reduction of the speed of the disc.
In the diagram of Fig. 116, the moving electrodes (mounted on the disc) are shown at
1, 2, 3, 4, etc. The spark, for example, passes from stationary electrode A to an electrode
on the disc, through the disc and out at electrode B. The effective length of the rotary
discharge gap is much greater than the actual distance between the stationary and revolving
electrodes would indicate; actually the spark discharge begins long before the electrodes
STATIONARY/
ELECTRODES
MUFFLING
DRUM.
Fig. 116 — 2 K. W. Synchronous Disc Discharger of the American Marconi Company.
are directly opposite. Hence for favorable working the minimum distance between the
electrodes should be about .005 inch. This will give a clear spark discharge and will not
subject the condenser to abnormal strain.
One great advantage of the synchronous discharger is that it permits the
handling of very large powers. In fact, the Marconi Company have constructed
and successfully operated such dischargers at 500 K. W. with marked results.
An additional advantage of this gap is that it prevents the oscillations in the
aerial circuit being retransferred to the closed circuit resulting in more efficient
radiation; in other words the quenching is reliable.
The one-half kilowatt sets of the American Marconi Company are fitted with
APPLIANCES FOR A RADIO TRANSMITTER. 105
synchronous dischargers which are practically a duplicate of the larger size gaps
such as furnished with the 2 K. W. sets.
(d) The construction of the quenched spark discharger is shown in Fig. 117
where a number of heavy copper plates separated by fiber insulating washers
micanite, or other insulating material, are placed in an iron rack and compressed
by means of a pressure bolt. The thickness of the wrashers is chosen so that the
space between the sparking surfaces of a single set of plates does not exceed .01
inch.
A groove is cut in each plate over which the inside edge of the washer rests.
This prevents the spark discharging at the very edge of the washer which would
Fig. 117 — Modern Quenched Spark Discharger with Motor Blower.
soon cause a short circuit. The insulating washers are specially treated so that
the discharge surface is airtight. This not only aids in quenching out the primary
oscillations, but gives a noiseless discharge as well.
It will be noted from the photograph, that the gap is cooled by a small motor-driven
blower mounted on the base which forces a draught of air through the base of the rack
against the cooling flanges of the plates.
Since the quenched discharger had been found to be effective with comparatively low
voltages, the potential of the transformer secondary rarely exceeds 15,000 volts, pressures
as low as 6,000 volts being frequently employed. Approximately 1,200 volts are required
for each gap and the number that will be used in any case depends upon the voltage of the
transformer.
The great advantage of the quenched gap lies in its ability to prevent the energy of
the oscillations induced in the aerial circuit being retransferred to the condenser circuit,
even when the oscillation transformer is closely coupled. Therefore the antenna oscillates
106
PRACTICAL WIRELESS TELEGRAPHY.
at single fundamental frequency and will radiate a single wave. The ideal spark gap
is one which permits the closed circuit to oscillate for a period of just sufficient length to
build up the oscillations in the aerial circuit to their maximum amplitude. Then the
oscillations in the condenser circuit should cease -, permitting the antenna to continue in
oscillation until its energy is dissipated.
If the coupling between the open and closed circuits is sufficiently loose, quenching of
the primary oscillations will be obtained with practically any type of gap but the advantage
of this particular type lies in the fact that quenching is secured with very close coupling,
which gives increased values of antenna current. The precise action taking place in a
transmitter employing a quenching gap can be shown as in Fig. 118 where a group of
oscillations in the open and closed circuits of a transmitter appear. It will be seen that
the closed circuit oscillates for a very brief period, or until the oscillations in the aerial
circuit reach their maximum amplitude after which the oscillations in the closed circuit
will be "quenched" out.
Summarizing the foregoing, it will be seen that the quenched gap offers sev-
eral advantages, if used in properly designed and tuned circuits :
(1) It is noiseless in operation;
(2) Has no moving parts;
(3) Permits the use of low voltage transformers;
(4) Gives synchronous discharges (when properly adjusted);
(5) Gives very large values of antenna current because of closer coupling.
The quenched discharger has not been found satisfactory for very high powers
and in such installations some form of the Marconi disc discharger is employed.
102. Adjustment of the Spark Note. — It is highly important that the
spark gap of any radio transmitter be ad-
justed to give a uniform discharge, having,
if possible, a musical pitch. A uniform
spark discharge not only permits the sig-
nals to be more easily deciphered at the re-
ceiving station through atmospheric or
static discharges, but also permits better
formation of the characters of the tele-
graph code on the part of the sending oper-
ator. In addition, the pitch of the note has
a marked effect on the response of the re-
ceiver telephone diaphragm, there being a
critical spark frequency for maximum re-
sponse with different types of telephones.
In the case of the plain spark discharger,
the pitch of the note while governed
primarily by the frequency of the alter-
nator, is also dependent upon other factors
such as,
(1) The length of the gap;
(2) The voltage of the generator;
(3) The capacity of the condenser;
(4) The design of the spark electrodes;
(5) The nature of the surrounding medium
whether gas or air.
Now the capacity of the condenser in
the usual radio set is a fixed quantity,
hence, the correct note for this gap is found
by increasing or decreasing the length of
the discharge gap or by adjustment of the
transformer voltage.
Blunt discharge electrodes give an ir-
regular spark note whereas sharp pointed
electrodes give a high pitched note, but they
generally diminish the amplitude of the
CLOSED
Fig. 118 — Showing the Oscillations in Closed and Open
Circuits of a Properly Adjusted Transmitter.
oscillation. A compromise between all these conditions is usually effected.
The correct spark tone for the rotary gap is obtained by adjusting the position of the
APPLIANCES FOR A RADIO TRANSMITTER.
107
stationary electrodes until synchronous discharges are obtained, and also by regulating the
length of the gap and the voltage of the transformer.
The note of the quenched gap is adjusted by variation of the number of gaps or by regu-
lation of the generator voltage. By proper adjustment, synchronous discharges are readily
obtained as will be evidenced by the uniformity of the note. (See Appendix, Section G.)
103. Oscillation Transformers. — The functions performed by the oscilla-
tion transformer of a radio-transmitter may be summed up as follows :
(1) Transfers energy from the closed circuit to the open circuit;
(2) Permits the wave length of either circuit to be increased or decreased (by
variation of the self inductance of either coil);
(3) Permits some adjustment of the damping of the oscillations flowing in the
aerial system.
The degree of coupling between the primary and secondary circuits of an
oscillation transformer can be altered in three ways:
(1) By drawing the windings apart mechanically;
(2) By variation of the self inductance of either winding;
(3) By turning one winding at a right angle to the other.
All three methods are in use. The oscillation transformer used in the 2 K. W. 240
,\ SEC,/
\ \ \ / / /
Fig. 120— Showing the Effect of Turn-
ing Secondary at Right Angles
to Primary.
cycle sets and the 60 cycle sets of the
Marconi Company is shown in Fig.
119. The primary winding has eight
turns of copper tubing approximately
15 inches in diameter, spaced 1 inch
apart, the tubing being about % inch
in diameter. The adjacent turns of
the primary winding are well insu-
lated by means of specially designed
porcelain insulators. The secondary is
made up of heavy stranded insulated
copper cable wound on a hard rubber
spool. Since the inductance of the secondary is fixed, variation of the fre-
quency of the oscillations is secured by adjustment of the aerial tuning inductance.
The secondary winding is mounted so that it can be turned at a complete right
Fig. 119 — Type A Oscillation Transformer of the
American Marconi Company.
108
PRACTICAL WIRELESS TELEGRAPHY.
angle to the primary or at any required intermediate position, which permits close
regulation of the transformer coupling. The effect of tilting the secondary at a
right angle to the primary is shown in Fig. 120 where the coupling is practically
zero. It will be seen that the lines of force of the primary are parallel with the
PRIM
COPPER STRIP,
VARIABLE
CONTACT
Fig. 121 — Showing Position of
Maximum Coupling of Type
A Oscillation Trans-
former.
Fig. 122 — Pancake Type Oscillation Transformer.
turns of the secondary and therefore no induc-
tion takes place in the secondary but in the posi-
tion, Fig. 121, the lines of force cut the secondary
turns at a right angle and the coupling is maxi-
mum.
In all transmitting sets it is advantage-
ous to ha\e the inductance of the primary
or the secondary winding continuously va-
riable, i. e., the construction must be such that
the entire inductance can be gone over inch by
inch with a sliding contact. An oscillation trans-
former of this type is shown in Fig. 122. The primary and secondary windings
consist of a spiral of copper ribbon placed edgewise on an insulating disc. The
handle is fitted with a sliding contact which permits any amount of inductance to
be inserted in the circuit, inch by inch. The same handle that varies the induct-
ance is used to draw the primary and
the secondary windings apart, thus
varying the coupling.
In a certain foreign radio system, an
inductance element known as a variometer
inductance is employed to change the de-
gree of coupling between the closed and
open circuits of radio-frequency. Briefly,
it consists of the windings A and B, Fig.
123, comprising two coils which can be
magnetically opposed to each other. The
coils are connected in series and when di-
rectly opposite the inductance is at a mini-
mum value, but when B is drawn away
from A the inductance gradually increases,
maximum inductance being obtained when
they are drawn completely apart.
If the variometer is connected In the
aerial system as in Fig. 124, and its self-
inductance gradually increased, the mutual
induction between the open and closed
circuits will be increased and therefore the FiS- 123— Showing Fundamental Principle of the Vario-
coupling.
To be efficient and to have a minimum resistance, variometers must be wound with
stranded copper cable made of a great number of small strands each of which is insulated
from neighboring ones. A stranded cable made in this way is called "Litzendraht" which
APPLIANCES FOR A RADIO TRANSMITTER.
109
affords a conductor of maximum con-
ductivity for high frequency currents.
Oscillation transformers may have
fixed values of inductance for both the
primary and secondary windings as in
Fig. 125. In one type, the primary has
a single turn of copper cable wound
around 6 or 8 turns of smaller cable,
constituting the secondary winding.
The coupling is rather loose — about 8
per cent, for the average aerial. The
necessary changes of wave length are
obtained by variation of the capacity of
the condenser in the closed circuit and
the inductance of the aerial circuit.
104. Aerial Tuning Inductance.
—The aerial inductance coil may be
of the continuously variable type
having a sliding contact which
bears on an edgewise copper strip
as in Fig. 126, or of the round barrel type made of stranded copper cable
Fig. 124— Showing How Coupling is Changed by Vario-
meter.
COPPER STRIP
Fig. 125 — Square Coil Type Oscillation Transformer.
as in Fig. 127. The inductance of
the latter type is altered by means
of a plug contact. It is, of course,
essential that adjacent turns be well
insulated from one another and
separated so that there will be no
sparking between them. Also the
coil must be mounted on an insu-
lated base or on specially devised
insulators to prevent the high volt-
age current leaking to nearby con-
ductors, or conducting material.
105. The Short Wave Con-
denser.— One form of this con-
denser as constructed by the Mar-
coni Company, has four glass plates
15 by 15 inches covered with tinfoil
12 by 12 inches. Each plate has a Fig. 126 — Continuously Variable Aerial Tuning Inductance.
110
PRACTICAL WIRELESS TELEGRAPHY.
capacity of approximately .002 mfds. and since four are connected in series, the
resulting value is .0005 mfds.
A very recent type of short wave condenser manufactured by the Marconi Company is
shown in Fig. 128. Four copper plated
glass jars are mounted on a metal rack
and connected together as follows: Con-
nection is made from the binding post E
of the left hand inside jar A to the aerial
system. The outer coating of jar A rests
on the inside coating of the jar B. The
outside coating of jar B makes contact
with the outside coating of the jar D
through the metal rack. The circuit con-
tinues on from that point in just the re-
verse direction, to that cited in the first
case, finally ending at the binding post of
jar C. The four jars are thus connected
in series and have combined capacity of
-
Fig. 127 — Drum Type Aerial Tuning Inductance.
.0005 mfds. The short wave condenser may be connected in series with either the aerial
wires or the earth lead.
106. High Potential Condensers. — The Leyden jar type of condenser has
been described in paragraph 84. The assembly of the flat plate condenser is
shown in Fig. 129 where three banks of condenser plates are connected in series.
The student should note from this diagram how the connecting tabs are brought
out from the sheets of tinfoil and the manner in which the plates are stacked up.
It will be seen from the detail that a
left hand tab plate is stacked up
against a right hand tab plate and so
on until the required capacity is ob-
tained. When one group is com-
plete, the entire unit is bound with
canvas tape and immersed in a tank
of oil.
The tinfoil is first attached to the
condenser plates by means of a good
grade of fish glue after which it is al-
lowed to dry. The plate is then coated
with shellac or hot paraffin and after dry-
ing again is ready for use.
Owing to the general inconvenience
of assembling, an oil condenser of this
type and the bother of replacing a broken
plate, in case of breakdown, it is grad-
ually being eliminated from ship sets. In
case of accident, the copper plated Ley-
Fig. 128 — Short Wave Condenser American Marconi
Company.
den jar affords a distinct advantage be-
cause a broken jar can be replaced within
a few minutes. In event the charging current exceeds 15,000 volts a series parallel connec-
tion of condenser plates is required. This connection divides the voltage between the two
banks and thereby reduces the strain on the dielectric.
Compressed air condensers are in use but the expense of construction does not warrant
their general adoption. Briefly, the construction is as follows : A number of interleaved
steel plates are enclosed in a cylindrical tank, one set of plates being insulated from the
structure. The tank is pumped to pressure of 250 pounds air pressure which has sufficient
dielectric strength to withstand potentials of 25,000 volts. The dielectric losses in a con-
denser of this type are, of course, zero and a permanent rupture of the dielectric medium
is not possible. The tanks are very cumbersome and some difficulty is experienced in
keeping them air tight.
107. High Frequency "Choking" Coils. —During the charge and discharge
APPLIANCES FOR A RADIO TRANSMITTER.
30,000 VOLTS
111
Fig. 129— Assembly of the Oil Plate Condenser.
of the condenser of the closed circuit, a back pressure is exerted on the secondary winding
of the high voltage transformer. Although the impedance of the spark gap circuit is so low
compared to that of the secondary winding of the transformer that the spark leaps the gap
in preference, the discharge of the condenser may cause sufficient difference of potential
between the turns of the
secondary units of the
transformer to puncture the
insulation and short circuit
adjacent layers. Possible
punctures from this source
may be obviated by means
of "choking" coils of rela-
tively high self inductance
connected between the
transformer and the con-
denser as shown at N1 and
N2, Fig. 130. These coils
consist of a few turns of fine
wire wound in the form of
a spiral, or in a single layer
on a porcelain, glass or hard
rubber tube. They offer but
little impedance to the low
frequency current flowing
from the secondary winding
Fig. i29a— Marconi Glass Plate Condenser of the transformer, but they
112
PRACTICAL WIRELESS TELEGRAPHY.
greatly impede the radio-frequency oscillations. Hence the secondary winding is protected
from injury.
108. High Voltage Transformers. — The construction of the open and
closed core types of transformers of the Marconi Company is shown in Figs. 131
and 132.
The primary coil of the open core transformer is wound on a core consisting of
a bundle of fine iron wires bound in circular form. The core is covered with
PRIM
CONDEN5EH
. Fig. 130 — High Frequency Choking Coils.
several layers of insulating tape followed by two or three layers of rather coarse
copper wire, such as No. 10 or No. 12 S. C. C. The entire primary is then in-
serted in an insulating tube. The secondary winding is composed of several sec-
tions, each consisting of a number of thin pancakes wound with rather fine wire,
such as No. 26 to No. 32.
Dry insulation is employed and in the larger sizes a blast of air is blown-
through the primary core to keep the transformer cool. The open core transform-
ers are designed for primary
potentials from 110 to 500
volts and for frequencies from
60 to 500 cycles. The sec-
ondary potential rarely ex-
ceeds 15,000 volts.
The transformer shown in
Fig. 131 is one of the open-
core type supplied with the
2 K. W. transmitters of the
American Marconi Company.
The primary core and wind-
ing are inserted in a Micarta
insulating tube, but the sec-
ondary turns are split into
groups, each consisting of
several small pancakes of fine
wire connected in series. The
secondary turns are covered
by an insulating tube which
is thoroughly clamped in
place. A safety spark gap
mounted on the top of the
transformer case has a third
electrode, which is connected
to earth. The primary termi-
nals are underneath the base
and the secondary terminals
Fig. 131—2 K. W. 500 Cycle Open Core Transformer. are mounted On the top.
APPLIANCES FOR A RADIO TRANSMITTER.
113
Fig. 132 shows the construction of the closed core transformers. The core
is rectangular and made up of thin sheets of iron which are insulated from one
another. The primary and secondary windings are mounted one over the other
on the middle leg. The entire transformer is immersed in a semi-liquid grease,
which softens at about 115 degrees Fahrenheit.
The closed core trans-
former is now supplied with
all Marconi sets. It has the
advantage of efficiency, and
cheapness of construction,
and requires but a small
amount of space for erec-
tion.
A safety gap is provided
to protect the secondary
winding in case, the rotary
gap is thrown out of
synchronism with the
charging current. In event
of such happening, the
spark will discharge across
the gap and also to earth
through a third electrode
(the metallic cone-shaped
projection on the case).
The transformer case is
connected to earth. If the
transformer is to be taken
apart to replace the wind-
ings, in cold climates, the
CASE.
Fig. 132 — Showing Construction of 2 K. W. Closed
Core Transformer.
case must be heated to melt the grease.
It is important that some part of the low frequency circuit of a radio-transmitter have a
certain amount of magnetic leakage when the transmitting key is pressed, for it will be
self-evident from the foregoing diagrams that when the spark discharges across the spark
gap, the secondary winding of the transformer is practically on short circuit. The ordinary
closed core transformer will under these conditions draw an excess of current with conse-
quent danger of burning it out. If the
transformer is provided with a magnetic
leakage gap such as the air gap A in the
transformer core, Fig. 133, the lines of
force generated by the secondary current
will take the path across this gap and in
consequence the self-inductance of the
primary winding will remain practically
constant. Even on direct short circuit of
the secondary, the transformer fitted with
1
"\ \
1
44
? (
PRIM
/
P
I™1*
( UJ
1 -4-
A |
44-
*£
•>
\
T-*
\
tl"
>
1 -
' 1
\
N*
^_
Fig. 133 — Closed Core Transformer with Magnetic
Leakage Gap.
magnetic leakage gap will not burn out,
and hence is particularly suitable for the
excitation of radio-transmitters. In the Marconi sets, the requisite amount of magnetic
leakage takes place at the generator, the armature being constructed to have very high values
of self-inductance.
The 2 K. W. 500 cycle transformers furnished with the Marconi panel trans-
formers require no external reactance coil except when the set transmits at the
wave length of 300 metres. To reduce the power for the reduced condenser
capacity at this wave length, a small fixed reactance coil is connected in series
with the primary winding.
114
PRACTICAL WIRELESS TELEGRAPHY.
WINDING
If the primary power is to be reduced by steps a reactance regulator is required
with any type of set.
109. Reactance Regulators. — The flow of current through an alternating
current transformer is preferably
regulated by a "choking" coil of
high self-inductance rather than by
a variable resistance. These coils,
which are termed choking coils or
reactance regulators, generally con-
sist of a few turns of heavy insu-
lated copper wire wound over an
iron core.
Two types are shown in Figs. 134 and
135. When an alternating current
passes through the coil, the correspond-
ing magnetic lines of force rise and fall
with the current, but the collapse of the
field sets up a counter E. M. F. which
acts as an effective resistance. The flow
Fig. 134— Primary Reactance Coil.
of current can be varied by a multi-
point switch as in Fig. 134, or by draw-
ing the iron core in and out of the windings as in Fig. 135. In the design of Fig. 135 a "U"
shaped iron core is inserted in two windings connected in series. The self-induction of the
coil is varied by moving the core in and out the windings.
Certain types of high potential transformers are designed for direct connection to the
power mains, and therefore they do not require a reactance regulator.
110. Aerial Changeover Switch. — The object of the aerial switch is to
connect the aerial alternately from the transmitting to the receiving apparatus.
Because of the potentials of the transmitting apparatus, the receiving apparatus
must be completely disconnected from
the transmitting aerial by a switch
with a break of at least 6 inches in
length.
An aerial switch of recent design, the
type S. H. switch of the Marconi Company
is indicated in Fig. 136 with the necessary
diagram of connections for a commercial
radio installation. When the handle of the
switch is thrown upward, the apparatus is
connected for receiving, but in the down-
ward position the transmitting apparatus
functions. The switch controls several
F,g. 135- J Shaped Reactance Coil. other important drcuits as well as the
aerial circuit connection. Thus when the switch is thrown to the transmitting position,
(1) Contacts A, B, close the D. C. circuit to the generator field;
(2) Contacts C, D, close the circuit to the automatic motor starter or to a motor
driven blower;
(3) Contacts E, F, close the circuit to the primary winding of the power trans-
former ;
(4) The spring contacts R, R, spring together and connect the transmitting
apparatus to the aerial system.
(5) The circuit to the primary winding of the receiving tuner is broken between
G and K;
(6) Contacts L and M place the detector on short circuit;
(7) Contacts N and O short circuit the telephones.
The reverse connections and disconnections, of course, take place when the switch is
thrown to the receiving position.
APPLIANCES FOR A RADIO TRANSMITTER.
115
TUNER
Fig. 136— Connections of a Modern Aerial Changeover Switch.
It will be evident from the foregoing that during the sending period at a given station, the
receiving tuner is thoroughly disconnected from the antenna and during the receiving
period the circuit to the field winding of the generator is interrupted because otherwise
the current flowing to the meters will induce interfering currents in the receiver which
may swamp out the radio signals ^ from a far distant station. Other types of aerial
change-over switches are described in Part IX.
111. Transmitting Keys.— The sig-
nalling keys for radio telegraphy are
of heavier construction than those used
in landline telegraphy because they are
required to interrupt large values of cur-
rent. It is found possible to break cur-
rent up to 35 amperes by a hand
manipulated key, but for current in ex-
cess of-this value, a magnetically operated
relay type of key is employed.
One type manufactured by the Mar-
coni Company appears in Fig. 137.
Fig.137~A Hand Manipu.a.ed Te.egraph Key. ^^ 4^ ^ad platinum pofnts for
breaking the current, but silver contacts of increased area have proven a satis-
factory substitute.
The circuit of an electromagnetic
key is shown in Fig. 138. A pair of
magnets M, M1 are wound to approxi-
mately 150 ohms resistance and con-
nected to 110 volts D. C. through a
small W. U. sending key. Extra large
contacts A, B are mounted on the arma-
ture and stationary posts which may
break 50 or 60 amperes without arcing.
Another type has a solenoid winding
with a plunger extending into a box of
oil. The contacts make and break the
circuit under oil, reducing arcing to a
minimum.
In certain high power stations spe-
cially constructed electromagnetic keys
interrupt the circuit from the secondary Fi* 138~ circuits of Ma*net5c
winding of the transformer instead of the primary. 500 kilowatts can be broken in this
manner.
1 10 VOLT D.C.
PART VIII.
AERIALS OR ANTENNAE
112. FUNCTION OF THE AERIAL. 113. DETERMINATION OF THE
WAVE LENGTH FROM THE DIMENSIONS OF AN AERIAL.
114. FUNDAMENTAL CONSIDERATIONS. 115. VARIOUS TYPES OF
AERIALS. 116. DIRECTIONAL AERIALS. 117. STANDARD MAR-
CONI AERIAL. 118. THE DECK INSULATOR. 119. INSTALLA-
TION OF THE AERIAL. 120. EARTH CONNECTION. 121. RADIA-
TION. 122. ANTENNA DECREMENT. 123. TRANSMISSION
RANGE.
112. Function of the Aerial. — The function of the aerial or antennae of any
given radio station is two-fold:
(1) To radiate energy in the form of electromagnetic waves;
(2) To absorb part of the energy of the waves sent out by the transmitter.
The stations employing two aerials, one for transmitting and one for re-
ceiving are few in number; in fact, the great majority of wireless stations employ
a single antenna for both purposes, which in its simplest form consists of a wire
of silicon bronze, copper or aluminum supported vertically by an insulator from
a mast or tower. The aerials for present day ship use consist of 2, 3 or 4 wires
connected in parallel with adjacent conductors placed from 2l/2 to 3l/2 feet apart.
Not all aerials, however, are supported vertically; the great majority have a
flat top portion which extends horizontally to a distance varying from 40 to 6,000
feet, the length depending upon the use to which the aerial is to be put or to the
power of the station.
Experimentation and reasoning show that the various types of aerials do not
radiate with equal intensity in all directions. A certain type, for instance, has a
distinctly directive characteristic and will radiate its energy more strongly in a
given direction. Still another type confines the greater part of its radiation to
two opposite directions. Not only does the factor of radiation require to be
taken into account but added to this are the tuning qualities of the radiated wave,
which are somewhat affected by the design of the aerial. It is, therefore, well to
review at once the factors governing the type of aerial adopted in any particular
case.
Chief among the controlling factors are :
(1) The space available for erection;
(2) The total expense of installation;
(3) The radiating properties;
(4) The desired characteristic of the radiated wave (whether "sharp," "broad"
or "directional").
Without regard to the foregoing considerations, the dimensions of an aerial
are governed :
(1) By the length of the wave to be radiated;
(2) By the space available for erection.
As we have shown, an aerial possesses both distributed capacity and induct-
ance which combined give it a defined period of oscillation when a charge of
electricity is applied to it. These oscillations will set up a wave motion the
length of which is related to the capacity and inductance of the system in the
AERIALS OR ANTENNAE.
117
following manner: If the capacity (C) be measured in farads and the inductance
(I.) in henries, the length of the wave will be equal to 4 X V X V LC, where
V = the velocity of electric waves in ether (300,000,000 meters per second).
Now the length of the radiated wave can be increased by connecting a coil of
wire (aerial timing inductance) at the base of the aerial, or decreased by con-
necting a condenser in series at the base, but there are certain limitations in either
direction as will be presently explained. Moreover with concentrated inductance
at the base of the aerial we can no longer use the simple formula above for de-
termining the length of the wave which must now be modified to read, wave
27T
length - - XV X V LC, where K is a certain correction factor the ratio of
K
the inductance of the coil to the total inductance of the aerial.
Experiment indicates that it is not advisable to load an aerial with inductance to radiate a
wave more than four times the natural wave length, because the insertion of greater amounts
will reduce the flow
of current considerably
and thereby reduce the
range of the trans-
mitter. In fact, the
maximum transmitting
range is obtained in
every case, when the
aerial radiates at a
wave length near to its
fundamental wave. The
use of localized induc-
tance decreases its de-
crement, but does not
add to the energy of the
oscillations. Hence,
large amounts of load-
ing inductance are, wherever possible, to be avoided. The addition of inductance in the
antenna circuit up to a certain point is favorable to the tuning qualities of the radiated wave,
but beyond this point, unless the capacity of the aerial be increased, the flow of current will
be reduced considerably.
A small amount of inductance is, of course, inserted at the base of the aerial to act as
the secondary winding of the oscillation transformer, but, generally, it need not exceed
10,000 to 15,000 centimeters. In all cases, the length of an aerial is governed principally
by the length of the wave to be radiated, but to permit the insertion of the secondary
inductance, the dimensions should be such that its natural wave length will be less than
the length of the radiated wave.
It is easily seen that if the length of the aerial be increased, both the inductance
and capacity will be increased and the radiated wave accordingly. Hence, if the
aerial is found after erection to be too long for the required wave, either the
length of the aerial can be reduced or the length of the wave can be artificially
reduced by means of a series condenser. Increased flow of antenna current will be
obtained in any case if an aerial is selected, the dimensions of which will permit
the required wave to be obtained without the series condenser, but aboard ship an
aerial of the correct dimensions cannot always be obtained ; in fact, a short wave
condenser is generally used for the 300 meter wave and a small amount of induct-
ance for the 600 meter wave.
113. Determination of the Wave Length from the Dimensions of an Aerial.
— The fundamental or natural wave length of an aerial can be computed directly from the
dimensions, the most notable contributions to the determination having been made by Prof.
G. W. Howe* and Dr. L. Cohen; but generally these formulae are too complicated for the
practical worker; hence, the following approximate method may be used. First, it may be
*cTw. Howe, Wireless World, Dec., 1914, Jan., 1915.
Fig. 139 — Vertical or Fan Aerial.
118
PRACTICAL WIRELESS- TELEGRAPHY.
INSULATORS
Fig. 140— Umbrella Type Aerial.
mentioned that the natural wave length of a four-wire horizontal aerial with the wires spaced
about 2l/z feet apart will be approximately 4.4 to 4.8 times the total length of the aerial, that is,
the length from the extreme end down to
the apparatus at the station house. This
factor is, of course, extremely approxi-
mate, for it does not take into account the
presence of nearby conductors, such as
chimneys, metal roofs, mast guys, trees,
etc., some of which have the effect of in-
creasing the capacity of the system.
For an aerial system comprising, let us
say, four wires spaced 2^2 feet apart, the
natural wave length is not much greater
than that of a two-wire aerial with equiva-
lent spacing, because although the addition
of wires increases the capacity slightly, it
also decreases the total inductance of the
system, and generally these two factors
nearly offset each other. Thus, in a given
instance, a two-wire aerial with wires
spaced 8 feet apart had a natural wave
length of 325 meters, and the addition of
two wires (inserted between) merely in-
creased the wave length to 345 meters.
If the 'wires of an aerial are widely
spaced apart, the capacity is greatly increased, and the total inductance somewhat increased,
due to the diminishing of the mutual inductance between adjacent wires. But the increase
of capacity exceeds the decrease of inductance, and the natural wave length will therefore
be increased considerably. In practice, it is the custom to space the wires so they will be
mutually inductive, the distance between adjacent wires not exceeding three feet.
114. Fundamental Considerations. — In the design of a wireless aerial the
important points to be considered are:
(1) The aerial wires must possess great tensile strength and be of good
conductivity;
(2) There should be several parallel wires;
(3) Adjacent wires should be spaced 2 to 3 feet;
(4) The wires must be thoroughly insulated at all points of support;
(5) If possible, the aerial should be erected in a clear space and at least a
half-wave length from all metallic structures.
The matter of antenna insulation is extremely important ; the antenna insula-
tors should not only possess high specific resistance, but they should also be of
considerable length to prevent the high voltage current discharging over them to
some nearby metallic conductor. Particular care must be taken to insulate the free
end of an aerial because, owing to the fact that the voltage and current are not
uniformly distributed in vertical aerials, a very much greater potential exists at
the top than at the base. This non-uniform distribution exists to some extent in
all types of aerials, but is less manifest in the flat top aerials than in vertical types.
Hence any conductors at the top or the free end of the aerial that would tend to
start leakage of the high voltage current should be widely separated and thor-
oughly insulated from the aerial wires.
115. Various Types of Aerials. — Four general types of aerials are in use:
(1) The vertical or fan aerial;
(2) The umbrella aerial;
(3) The inverted "L" flat top aerial;
(4) The "T" aerial.
(a). The vertical cwrial shown in Fig. 139 consists of a fan or harp of copper
or silicon bronze wires held vertically into space by a wooden mast, a steel tower
or any convenient structure of sufficient height. The wires of the harp may or
may not be joined at the top. All wires, however, must converge at the lower end
AERIALS OR ANTENNAE. 119
where they enter the station house and are connected to the apparatus. The free
end of the vertical aerial must be well insulated to prevent direct leakage to the
supporting halyards or stays, and at the lower end the wires must be stayed to
take the strain off the station house roof insulator.
Although the ver-
tical aerial is ac-
knowledged to be
the best radiator
of electromagnetic
waves practically
equal results can be
obtained from a flat
top aerial (of
increased d i m e n -
sions) with a less
expensive supporting
Fig. 141— Inverted "L" Flat Top Aerial. Structure.
tive of the degree of
efficiency obtained, a vertical aerial could not possibly be used aboard vessels on
account of the derrick booms, mast guys and smoke funnels which take up the
space that would be required for erection:
(b). The umbrella aerial shown in Fig. 140 receives its name from its general
shape and similarity to an umbrella. It will be noted in this diagram that a number
of wires spread radially in several directions from a common center at the top of
the mast, and that a wire extends therefrom to the apparatus in the station house.
The ribs of the umbrella generally are about two-thirds the length of the mast, but
the guying out wires must be six to seven times the length of the vertical part.
Although it has been found to be of some value for portable military sets, the
umbrella aerial is scarcely employed in commercial working except in certain high
power stations designed and erected by German engineers.
(c). The inverted "L" flat top aerial of Fig. 141 is almost universally em-
ployed for ship service. It consists of a number of parallel wires stretched between
two masts and attached on either end to wooden or metal spreaders, which are
thoroughly insulated from the supporting halyards. The horizontal wires A to B
are called the "flat top portion" and the vertical wires, the "lead-ins."
The lead-in wires, which should have equal conductivity to the wires in the
flat top, are attached to one end of the horizontal wires, then passed through a deck
insulator and finally connected to the apparatus within the station. The flat tops
of the ships under control of the Marconi Wireless Telegraph Company of America
vary from 75 to 250 feet in length and the lead-ins from 70 to 150 feet.
If the lead-ins are attached to the center of the flat top, as in Fig. 142, the aerial
is said to be of the "T" type.
Either "T" or "L" aerials are almost universally employed on vessels, princi-
pally because they are more convenient to install. Those in the Marconi service
have 2, 4 or 6 wires ; the majority, however, have four wires spaced from 2^2
to 3y2 feet.
The fundamental wave length of the "T" aerial is invariably less than that of
the inverted "L" type of the same dimensions. When the lead-ins of a given aerial
are removed from the end of the flat top and attached to the center, the total in-
ductance will be less than with the previous connection, and since by this change,
the capacity of the system remains practically unchanged, the length of the radiated
wave will be less than in the case of the "L" aerial. This is easily understood if
viewed in the following manner : Beginning at the point where the lead-ins are at-
tached, the two ends of the flat top may be considered as two aerials in parallel,
and as is well known, the inductance of two parallel conductors is less than that
120
PRACTICAL WIRELESS TELEGRAPHY.
a
Fig. 142— -T" Flat Top Aerial.
of either taken separately; therefore, the total inductance of the antenna will be
reduced and the radiated wave accordingly.
To illustrate the point: A four-wire inverted L type of aerial, 100 feet in length, 60 feet
in height, has capacity of .0004 microfarads, and inductance of 62,000 centimeters. A "T"
aerial of the same dimensions has capacity of .0004 microfarads, and inductance of 37,000
centimeters. Keeping in mind the simple formula (X = 38 x VLC) for computing the wave
length of a radiative oscillator, the change in wave length brought about by this connection
is easily determined. The wave length of the "L" aerial will be approximately 188 meters
and of the "T" aerial, approximately 145 meters.
Since the standard transmitters of the Marconi Company are designed for the
use of the 300, 450 and 600 meter wave, the precaution must be taken to select
an aerial of such dimensions that a moderate degree of efficiency will be obtained
on the two shorter
waves and the maxi-
mum degree of effi-
ciency at the longer
wave; that is, we
must provide an aer-
ial that will give the
highest possible aer-
ial current for each
of the three standard
waves. An aerial
having a fundamen-
tal wave length ap-
proximating 325 me-
ters gives good values of antenna current at the 450 meter and 600 meter adjust-
ment, and a fair value at the 300 meter wave adjustment, but an aerial of correct
dimensions for this fundamental wave length obviously cannot always be erected.
On certain large vessels, the distance
between masts is so great that if the
wires were suspended the total length
between them, a series condenser would
be required for the 600 meter wave. Be-
cause the wave length of an aerial can
never be reduced by a series condenser
to less than one-half its natural length,
the 300 meter wave could not be obtained
in a case of this kind, and it would there-
fore become necessary to cut off a por-
tion of the horizontal wires, to keep the
radiated wave within limits. It is usual
in such cases to stretch the wires from
mast to mast and insert an insulator
about 50 to 100 feet from one end or at
such distance as will permit the required
length of wave to be obtained. On the
other hand, the aerials of small vessels,
such as tugboats, etc., have to be loaded
with large amounts of inductance to ob-
tain the 600 meter wave. On such ves-
sels the aerial is frequently made up of
eight wires in order to obtain the maxi-
mum possible capacity.
With few exceptions, all ships' aerials
in the Marconi Service require a short F»&- 143— Bellini-Tosi Directional Aerial,
wave series condenser for the 300 meter
wave, but should the aerial be found upon measurement of its wave length to require a
series condenser for the 450 meter wave, either the length of the flat top would be reduced
5PARK GM>
Height of
No. of
Natural wave
Capacity
flat top.
wires.
lerg'.h.
mfds.
96ft.
6
374
.00128
125
6
368
.00145
87
4
355
.00115
95
4
412
.0015
90
6
360
.0015
100
6
325
.00132
92
4
285
.00075
150
4
426
.00096
90
6
360
.0023
55
6
230
.00085
110
6
290
.0009
98
6
425
.0024
85
4
380
.00082
AERIALS OR ANTENNAE. 121
or the lead-ins be attached to the center. The general rule adopted by the American Mar-
coni Company is as follows : If the length of the flat top is less than 125 feet, the inverted
L aerial is employed, but if it exceeds 125 feet, the lead-ins are attached to the center. This
permits the use of the three standard waves, gives good values of antenna current and
affords a very favorable decrement of the oscillations.
As a matter of general information we may cite examples of actual measurements of
the wave length of commercial ships' aerials. This data appears in the following table:
Length of
Type. flat top.
L 208 ft.
T 200
L 150
T-Imp. 250
L 200
L 120
T 130
T 250
L 200
L 125
T 151
L 200
L 170
We see from this table that the capacity of some aerials is rather large, but
generally this increase is due to the presence of nearby metallic structures of some
sort, such as mast guys, derrick booms, or steel masts.
We may sum up the advantages or disadvantages of the various types of aerials briefly,
as follows : The vertical aerial is a very efficient radiator of electric waves ; but if large
amounts of energy are to be radiated, a large aerial and a very high supporting structure
are required ; the cost of the latter may be prohibitive. The umbrella aerial does not quite
possess the radiating properties of the vertical aerial and due to the fact that the ribs of
the umbrella must be guyed out several hundred feet from the base of the supporting
mast, a large area is required for its erection. But with this disadvantage, the umbrella
aerial is found to be of some value in portable military stations, where the ribs of the
aerial act as guy supports as well as radiators of the electric waves.
The "L" and "T" aerials also do not radiate quite as efficiently as the simple vertical aerial
of the same dimensions, but they have slightly lower njS^ral decrements, and therefore, radiate
a sharp wave with less localized inductance. Flat top aerials can be erected at much less
expense than vertical aerials of much less length and they prove to be just as effective
at less initial expense. Over all, it must be kept in mind that irrespective of the degree
of efficiency obtained, the flat top aerial only can be conveniently employed aboard ship.
Wave Distortion. — Better signals are frequently obtained from a given
transmitter by the use of a receiver aerial, a part of which is horizontal such as the "L"
and "T" types. This may be accounted for in the following way: It has been assumed
by several investigators that the lower end of the loops of force or ether strain radiated
by an aerial are retarded in their propagation over dry earth, e. g., the lower part travels
more slowly than the upper part, which causes the field of the radiated wave, so to speak,
ta be tilted against the direction of movement.
In any receiver aerial the greatest amount of energy is taken from the passing wave
when the wires are at right angles to the magnetic field and parallel to the static field.
It necessarily follows that if the loops of force radiated from the aerial of Fig. 99 do not
hold their vertical position but are tilted forward, better distances would be covered, in
fact, more energy would be induced in the receiver aerial, if part of it were vertical and
part horizontal.
116. Directional Aerials. — It has been definitely proven by Marconi that a
horizontal aerial in which the length of the fiat top largely exceeds the height will radiate
more strongly in the direction opposite to the free end. Also the strongest signals will be
obtained at the receiver by an aerial, the free end of which points in the direction opposite
to the free end of the transmitting aerial.
Taking full advantage of the unsymmetrical radiation from such aerials, the high power
transoceanic stations of the Marconi Company employ directional aerials exclusively. The
PRACTICAL WIRELESS TELEGRAPHY.
AERIALS OR ANTENNAE.
123
flat tops of such aerials are from 3,000 to 6,000 feet in length, and from 300 to 450 in
height. The fundamental wave length is close to 10,000 meters.
The greater part of the energy radiated from a transmitter may be confined to a given
direction by the use of the Bellini-Tosi aerial shown in Fig. 143. A triangular aerial,
A, B, C, is supported by a vertical mast. The two sides of the rectangle A, C. and B, C.
make an angle of 30° with the vertical, and the third side is horizontal to the earth with
the coil L-l inserted at the center. L-l is inductively coupled to a spark transmitter and
tuned to syntony. An aerial of this type will radiate its energy with greatest intensity in
the direction of its own plane, the radiation in a direction perpendicular to the triangle
being zero. In any direction making an angle 0 with the plane of the triangle, the intensity
of the radiation varies as the cosine of the angle 0. The triangular aerial may be used
for receiving purposes as well, and if the aerial be arranged so that it can be turned on
its axis the greatest strength of signal will be obtained when the plane of the antenna
points in the direction of the wave front. In modified form these aerials are made use of
in connection with the Marconi direction finder, which will be described in Part XIII.
117. Standard Marconi Aerial. — Now that the fundamental design of the
various aerials has been shown, the construction of a standard Marconi ship's
aerial (American Marconi Company) will be described in detail. It will be noted
from the diagram of Fig. 144 that the flat top contains six silicon bronze wires, each
containing 7 strands, No. 18 wire. The wires are preferably equally spaced and
are attached to spruce spreaders from 14 to 18 feet in length which in turn are
attached to the running halyards by a bridle which is made up of strop insulators.
These insulators consist of ^j inch Russian boat rope which is partly covered by a
hard rubber tube. The space between the tube and the rope is filled with hot
sulphur which when cold, hardens and keeps out moisture. Both ends of the bridle
terminate in 'a heart-shaped shackle to which a galvanized steel halyard wire for
raising and lowering the aerial is attached.
To prevent the spreaders from swaying, side stays are attached to the ends (of
the spreader) and fastened to the mast. Twenty- four-inch hard rubber rod insu-
lators are inserted in
the rope to prevent
leakage of the cur-
rent in wet weather.
It will be seen also
that each wire of the
aerial is insulated by
a 2-foot hard rubber
rod which is at-
tached to the spread-
er by an eyebolt.
The lead-in wires
are attached to one
end of the flat top
and fastened to the
deck or cabin insu-
lator. To remove
the strain from this
insulator, two hard
rubber rod insulators are attached to the aerial and fastened to the deck by a wood
screw as shown in the drawing. Positive connection is made between the lead-ins
and the flat top by means of a Mclntyre connector shown in the detail of Fig. 144A.
The general design shown in Fig. 144 is not always duplicated in detail, but
wherever possible it is adhered to.
118. The Deck Insulator. — The transmitting aerial must be well insulated
at the point where it enters the radio operating cabin by an insulator that will with-
stand at least 30,000 volts. One form of deck insulator is shown in Fig. 145. A
FLAT TOP WIRE.
THESE ENDS SHULO
BE AT LEAST 10" LONG
MAC INTYRE SLEEVES.
DOUBLE TUBE fOR
*7- 18 WIRE SOLDERED
NOT TWISTED
Fig. 144a — Mclntyre Sleeve Connector.
124
PRACTICAL WIRELESS TELEGRAPHY.
CrO
Fig. 145— Bradfield Type Deck
Insulator.
long hard rubber tube T about 2 inches in diameter has
a brass rod extending through it which terminates at
each end in a wire connecting lug, W . The tube is
threaded at the center to take two wooden blocks A, B,
one of which is placed above the deck, the other under-
neath. After these blocks are drawn up tightly, the
wood screws are inserted. To insure a watertight joint,
a piece of canvas strip is placed underneath the blocks
and thoroughly covered with white lead. A metal
hood, H, fastened to the exposed end of the tube pro-
tects it from dampness.
The latest type of deck insulator is shown in Fig.
146, wherein a large electrose insulator has a heavy
brass rod moulded securely into it which terminates at
either end in a connecting lug. The outside of the insu-
lator is threaded, and after it is inserted in the hole in
the deck, it is drawn up tight by the collar, R, which is
threaded on the inside. Other types of deck insulators
are in use, but those just described are indicative of
modern practice.
119. Installation of the Aerial. — The aerial of a
ship should be installed, if possible, in such a way that
the lead-ins will be free and clear of all mast guys or
derrick booms. The further removed they are from
parallel conductors of any kind, the less will be the
danger of induced currents.
In measuring off the length of the flat top wires, approximately ten feet must be al-
lowed at each end for the bridle, the insulators and the reef block; hence 20 feet must
be subtracted from the distance between masts
at the start. The distance between masts can
generally be obtained from the ships' plans
or by actual measurement from mast to mast
on the deck. Each wire is accurately meas-
ured between two points marked off on the
deck and the wire cut and attached to the
insulators. Six or eight inches must be al-
lowed for serving the wire through the eye
of the antenna insulator.
All connections are thoroughly made on
the deck, after which the halyards are passed
through the reef block and fastened to the
shackle on the bridle. The aerial is then pulled
into space, it being freed from all obstructions
by three or more assistants.
120. Earth Connection. — The con-
nection from the transmitting apparatus
to the earth plate should be direct as pos-
sible and the conductor should be one of
high conductivity. In marine installa-
tions the earth wire is simply fastened to
the metal bulkhead by a bolt, the earth
connection being thus made through the
hull. Usually this connection is not more
than two or three feet in length.
On wooden vessels connection is made
to the propeller shaft in the engine room Fig. i46— Electrose Moulded insulator.
BRASS ROD
LUG
UBBER
AERIALS OR ANTENNAE. 125
or to the water drip at the smoke funnels. Installations grounded or earthed in
this manner generally do not transmit as far as those on vessels with steel hulls.
Occasionally a wooden vessel is placed in drydock and 200 or 300 feet of copper or
yellow metal nailed on the bottom for an earth capacity. A strip of copper is then
led from it to the radio cabin.
The earth plate for the land station is sometimes very elaborate and may consist of a
great number of copper or zinc plates buried in moist earth to a depth of several feet. Tn
addition a number of wires are spread radially from the station in all directions, being laid
particularly directly underneath the flat top portion of the aerial. If the station is located
on rock or dry soil, the earth wires are merely laid on the surface of the ground under-
neath the aerial. All wires are then joined to a common terminal and connected to the
apparatus in the station.
The earth plates and connections at the Marconi trans-atlantic stations are very elabo-
rate and expensive. A number of zinc plates are laid in a circle of 100-foot radius, the
transmitting station being situated at the center. About 250 copper cables connect from
the transmitting apparatus to each of the zinc plates. A number of copper cables stretch
out radially from the zinc plates, some of which lie directly underneath the aerial. In
addition, a number of wires may be laid directly underneath the aerial on the surface of
the ground.
If the ground is particularly damp or marshy, modified arrangements may be used.
121. Radiation. — As shown by Fleming and other investigators, the power
of the waves radiated from an aerial may be expressed as follows :
h2
W = 1578 X — X 1L'
\-
where W = energy radiated in watts ;
h = height of aerial in meters ;
X — wave length of aerial in meters ;
I r= current in amperes at the base of the aerial.
For example, if an aerial 40 meters (130 feet) in height, radiates at the wave length
of 600 meters and the aerial current is 10 amperes, the energy thrown off in the form of
402
electric waves = 1578 X -- X 102 = 694 watts.
6002
This equation is based on the assumption that the current is uniformly distributed
throughout the oscillator, which is not strictly true in all types, the distribution varying
widely according to the form of the antenna. Hence, in order that the power of the
radiation may be determined with any degree of accuracy, the average value of the current
must be determined, and this, of course, will be less than the current at the base of the
aerial.
2 1
The average value depends upon the form of the antenna, varying from — to — times
TT 2
the current at the base. If we denote the form factor of the aerial by the notation 1'" the above
formula should be 'Written ;
h2
W = 1578 - F' I L>
\-
This can be written :
W -.-. 1578 X
In this equation (F h) is the effective height of the aerial (the form factor multiplied
by the height) and in the case of the flat top antenna, the value of h is taken as the
height of the vertical portion only; also the form factor (F) merely takes into account
the average value of current in the vertical part of the aerial.
The student will note that if the average value of current in the antenna circuit remains
constant, the amount of energy radiated from a given aerial system depends directly upon
the effective height. and inversely upon the length of the radiated wave.
126 PRACTICAL WIRELESS TELEGRAPHY.
The following formula* is applicable for calculation of the form factor of any flat top
aerial oscillating near its natural period:
/ L\ f h v
F = 0.637| 1 + — JSin I I 90°*
V h/ Vh-r-L/
where L = length of the horizontal part for inverted L aerials and
equals one-half total length flat top for T aerials,
h =. height of vertical portion.
For example, if we had an aerial 100 feet in length, 60 feet in height, the value of the
form factor,
100 v s 60
= 0.637
/ 100 , 60 \
( 1+- \ Sin | - — 190°
V 60 / V 60 + 100 /
= 0.637 X 2.6 X Sin (0.375 X 90° )"
= 0.89
Now, if this aerial is worked near to its fundamental wave length, say 320 meters, and
the current oscillating in the aerial circuit is 6 amperes, the power thrown off in electric
waves,
= 1578X f °'92 x 18-4 V X 36 = 150 + watts.
V 320 /
122. Antenna Decrement. — The damping of the oscillations flowing in the
transmitting aerial is principally due to:
(1) Energy lost by radiation;
(2) Energy lost by resistance of conductors and earth plate;
The energy lost by radiation, is useful energy because it goes to make up the
wave motion, but the other two losses detract from the efficiency of the set and
therefore should be reduced to the lowest possible value. The resistance of the
aerial conductors can be reduced to a minimum by using a number of stranded
copper wires connected in parallel and in the average case the high frequency re-
sistance will then not exceed two or three ohms. The earth plate resistance is
reduced by an extended net work of conductors preferably buried in moist earth.
With an improperly adjusted transmitter there will be an additional source
of antenna damping due to the re-transference of energy to the spark gap cir-
cuit. This may be prevented by properly adjusting the spark gap and coupling
at the oscillation transformer.
The decrement due to radiation is usually determined by the insertion of
localized inductance and the amount of inductance required for a given radia-
tion decrement varies slightly with the construction, i. e., the form factor of
the antenna. The antenna is so designed that an inductance which will give
the correct wave length will also give the desired decrement when a properly
adjusted transmitter is employed.
Since the energy radiated in the form of electric waves causes damping of the oscilla-
tions in the aerial circuit, the loss of energy by radiation may be expressed as an effective
resistance or, in short, "radiation resistance," which, of course, will be expressed in ohms.
The radiation resistance is the quantity which multiplied by the square of the average cur-
rent in the aerial enables us to determine the power of the radiated waves.
The radiation resistance of a flat top aerial is expressed,
Where R = resistance in ohms ;
Fh=: effective height of aerial;
X = wave length in meters.
Hence an aerial, the effective height of which is 40 meters, operated at the wave length
of 600 meters, will have radiation resistance of
*A. S. Blatterman, Oct., 1916, issue of the Wireless Age.
AERIALS OR ANTENNAE. 127
402
1578X = 6.9 ohms.
6002
We see from this formula that the radiation resistance of an aerial depends directly
upon its effective height and inversely as the length of the radiated wave. It is also clear
that increase of the height will increase the wave length as well, and, therefore, the increase
of the power of the radiation will not be so large with an increase of height as might be
expected at first sight.
The radiation resistance (or radiation coefficient) of the vertical or fan aerials is gen-
erally higher than that of the flat top aerials, but, as mentioned previously, the flat top
aerials are less expensive to erect, more convenient to install and since the radiation resist-
ance should in any case be reduced by inductance, they are more desirable.
We want the radiation resistance of an aerial to be as high as possible so long
as it does not seriously damp out the oscillations and spoil the tuning qualities of
the wave; on the other hand we want the frictional resistance (including the con-
ductors and the earth plate) to be as low as possible.
The oscillations of the antenna circuit will be less feebly damped, if a certain amount
of inductance is inserted at the base but after a certain critical value is reached, the flow
of antenna current will be reduced which will reduce the power of the radiated waves.
The critical value can be determined in any case by noting the reading of the aerial
ammeter and determining the decrement of the oscillations by a decremeter. If a feeble
decrement is obtained at the expense of antenna current, the efficiency of the set will be
reduced.
If the effective capacity (C), the effective inductance (L) and the effective resistance
(R) of an aerial are known, the decrement per complete oscillation of the antenna circuit
can be calculated by the formula previously given.
s=irR|/|_
where C = capacity in farads ;
L — inductance in henries.
Now L and C can be measured by a wavemeter as will be shown in Part 11 and the
effective value of R can be determined in the following manner : A closed oscillation circuit
containing a quenched spark discharger is inductively coupled to the antenna circuit
with an ammeter connected in series. At any particular value of primary power, the
reading of the aerial ammeter is observed. A closed oscillation circuit having inductance
and capacity of the same value as the aerial is now connected across the secondary winding
of the oscillation transformer with the ammeter and a variable resistance in series. The
closed circuit is set into oscillation and the resistance is adjusted until the ammeter gives
the same reading as when connected in the antenna circuit. Obviously the value of R equals
the total effective resistance of the aerial. The student having had some experience in radio
will recognize this last circuit as the usual, "dummy aerial" which is employed in the
laboratory to make experimental determinations.
Assume for example that an aerial has effective capacity of .001 microfarads, effective
resistance of 7 ohms and effective inductance of 100,000 centimeters, then
/ .000,000,001
Decrement = 3. 1416 X 7X \ ~ — OOOT~~ ~-^8 per complete oscillation.
A decrement of this magnitude is very favorable to non-interference of radio stations
and is easily obtained with properly adjusted spark transmitters.
123. Transmission Range — It has been found that for a given length of
wave radiated from the transmitter, there are certain heights of sending and receiving
aerials, which will give the best signals over a given distance. The equation express-
ing the relationship of these quantities is as follows:
T __ 635 X I* X hs X hr . —0.0762 X d
*Xd t V X
Where I8 = current in sending aerial in amperes ;
Ir= current in receiving aerial in milliamperes ;
hs and hr= height of sending and receiving aerial in feet ;
X — wave length of transmitter and receiver ;
d = distance between in miles.
128
PRACTICAL WIRELESS TELEGRAPHY.
The value of the receiver current Ir is that to be obtained when the resistance of the
receiving aerial is 25 ohms.
If the resistance is greater or less, the factor 635 will be changed accordingly. The
factor 0.0762 is the coefficient of absorption which denotes the rapidity with which ether
waves are absorbed when travelling over sea water.
If we assume that 10 micro-amperes of current in the receiving aerial will create a just
audible signal and 40 micro-amperes, a readable signal, the required antenna current at the
sender for a given strength of signal in the receiver is readily obtained if the remaining
factors in the equation are known. The formula is still the subject of considerable debate.
Fig. 146a — 3 Kilowatt Non-Synchronous land station
type of transmitter (American Marconi Company).
PART IX.
RECEIVING CIRCUITS, DETECTORS AND
TUNING APPARATUS
^
STANDARD MARCONI RECEIVING SETS.
124. IN GENERAL. 125. THE PROBLEM. 126. SIMPLE
RECEIVER. 127. THE INDUCTIVELY COUPLED RECEIVER. 128.
OTHER METHODS OF COUPLING. 129. THE CARBORUNDUM
DETECTOR AND TUNING CIRCUITS. 130. ADJUSTMENT OF THE
INDUCTIVELY COUPLED TUNER. 131. THE ACTION OF THE CAR-
BORUNDUM CRYSTAL. 132. ADJUSTMENT OF CRYSTAL DETECT-
ORS. 133. DETECTOR HOLDERS. 134. CLASSIFICATION OF THE
RECEIVING DETECTORS. 135. FLEMING VALVE DETECTOR AND
TUNING CIRCUITS. 136. MARCONI TYPE 107-A TUNER. 137.
MARCONI MAGNETIC DETECTOR AND THE MULTIPLE TUNER
CIRCUITS (ENGLISH MARCONI COMPANY). 138. THE MARCONI
TYPE 106 RECEIVING TUNER. 139. MARCONI RECEIVING
TUNER TYPE 101 (AMERICAN MARCONI COMPANY). 140. THE
MARCONI UNIVERSAL RECEIVING SET (ENGLISH MARCONI
COMPANY). 141. ELECTROLYTIC DETECTOR. 142. THE THREE
ELEMENT VALVE DETECTOR. 143. A REPEATER VACUUM
VALVE CIRCUIT. 144. THE VACUUM VALVE AMPLIFIER. 145.
AMPLIFICATION OF RADIO FREQUENCIES. 146. THE EFFECTS
OF DISTRIBUTED CAPACITY. 147. THE "END TURNS" OF A
RECEIVING TUNER AND END TURN SWITCHES. 148.
THE VARIATION OF A RADIO FREQUENCY INDUCTANCE.
149. BUZZER EXCITATION SYSTEMS. 150. RECEIVING TELE-
PHONES. 151. MICROPHONIC RELAYS OR SOUND INTENSIFIERS.
152. BROWN AMPLIFYING RELAY. 153. ATMOSPHERIC ELEC-
TRICITY. 154. THE MARCONI BALANCED CRYSTAL RECEIVER
(ENGLISH MARCONI COMPANY). 155. TYPE I AERIAL CHANGE-
OVER SWITCH. 156. MARCONI TYPE 112 RECEIVING TUNER.
156A. GENERAL ADVICE FOR THE MANIPULATION OF A RECEIV-
ING TUNER.
124. In General. — Told in brief, the function of the receiving aerial is
to absorb a certain amount of energy from the advancing electromagnetic wave
in the form of radio-frequent oscillations; but more specifically, the wave motion
induces radio-frequent oscillations in the receiving- aerial, and a part of their
energy is made to operate some sort of signal making instrument within the
station.
We have already shown an electromagnetic wave to be composed of an electro-
static and an electromagnetic field, the former being radiated (in the case of the
vertical aerial) perpendicular to the earth and the latter at right angles to the
transmitting aerial and horizontal to the earth. It appears that the maximum
induction would be obtained at the receiving station if the aerial were of such
shape or lay in such position that it would be at right angles to the magnetic field
and parallel with the static field. But if we take into account that the radiated
130
PRACTICAL WIRELESS TELEGRAPHY.
Li
wave is distorted when propagated over dry earth, for example (base travelling
slower than top), it is easily seen that an aerial having a part horizontal and a part
vertical will receive the maximum induction therefrom.
The necessity for electrical resonance in circuits of radio-frequency in which energy
is transferred by coupling magnetically one to the other, has been explained
in detail. In fact, for the maximum induction, it is just as essential that
two open circuit oscillators be adjusted to substantial resonance as two
closed circuit oscillators. Only by tuning the receiver aerial to the natural
frequency of the transmitter aerial will the oscillations induced in the
receiver antennae attain their maximum amplitude; at all other adjustments
(of the receiver aerial) the strength of the induced current will be less,
depending upon the amount of detuning at the receiver.
Now the dimensions of receiver aerials differ widely, and, as
may be expected, the circuit of the receiver antenna contains appli-
ances whereby the oscillating period may be artificially increased or
decreased to conform with the frequency of the advancing wave
motion. These tuning devices are known as :
(1) The aerial tuning inductance;
(2) The short wave condenser.
By proper adjustment of these tuning elements the receiver
aerial can be electrically tuned to the wave radiated by the distant
transmitter. The advancing wave will then induce currents at a
rate tending to build up the amplitude of the receiver current — that
is, each half wave will have completed its work on the receiver
aerial before the next half wave acts. But under conditions of
dissonance between the transmitter and receiver aerials, the react-
ance of the receiving antenna circuit will not permit the induced cur-
rent to build up to its maximum strength.
The position occupied in the antenna circuit by these tuning
elements is shown in Fig. 147, where the aerial tuning inductance
is indicated at L-2 and the short wave condenser at C. The third
coil in this diagram, L-l, is employed to transfer the oscillations
induced in the antenna circuit to a local detecting circuit, where they
are translated into intelligible signals. Just as in the case of the transmitter aerial,
the aerial tuning inductance increases the fundamental period of oscillation of the
receiver aerial, but in this case makes it responsive to long waves, while the short
wave condenser decreases the fundamental oscillating period, making it respon-
sive to waves shorter than the fundamental wave of the receiver aerial.
Starting at the transmitting apparatus, the entire process involved in the induction of
oscillating currents in a receiver aerial may be summed up as follows :
Assume a transmitter at the sending station of the 500-cycle synchronous spark type,
giving 1,000 sparks per second. Each spark discharge will induce in the transmitter
aerial a single group of radio-frequent oscillations, and each group will consist of from
25 to 100 complete oscillations, varying in number as the decrement. These oscillations
will radiate a part of their energy in the form of a wave motion, and ^he Jength of a
single wave will be equal to their velocity per second, divided by their number. If the
receiver aerial is adjusted to electrical resonance with the oscillations of the transmitter,
1,000 groups of radio-frequent oscillations will be induced therein per second, . and by
appropriate devices they can be made to operate some sort of a signal making instrument,
such as a telephone receiver.
The coils L-l and L-2 and the variable condenser C are often termed the
frequency determining elements of the receiving system, because they permit the
natural oscillation frequency of the receiving aerial to be changed over certain
given limits. In contrast to the coils of the transmitting aerial circuit, the induct-
ances L-l and L-2 are made of fine wire rather than copper tujbing or heavy
stranded cable. A typical variable condenser of the type employed in the Marconi
wavemeter and receiving tuners is shown in Fig. 147a.
Fig. 147— Di-
agram Showing
Apparatus In-
cluded in the
Open Circuit of
a Receiving Set.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS. 131
125. The Problem. — The relationship between the wave length (A) the
oscillation frequency (N) and the velocity of electric waves (V) has already been
explained, namely:
V
300,000,000
Kence for the 600 meter wave N = - - = 500,000 cycles per second,
600
and accordingly for 300 meter waves N = 1,000,000 cycles per second. Then, to be
placed in resonance with the transmitter aerial, the receiver aerial must be. ad justed
in a way that if it were transmitting electric waves, the corresponding oscillation
frequencey, in the case of the 600 meter wave, would be 500,000 cycles, and for
the 300 meter wave, 1,000,000 cycles.
Assume that the receiver antenna has been adjusted to the frequency of the
transmitting station by means of the variable elements of Fig. 147, then the prob-
Fig. 147a — Variable Condenser for Receiver Circuits.
lem remaining is to make audible the feeble currents induced in the receiver aerial
or at least to make known their presence by some sort of a current indicator.
The ordinary magneto telephone receiver is a very sensitive indicator of electric cur-
rent, but experiment teaches that the maximum response is obtained from this instrument
when an alternating current or an equivalent fluctuating direct current of a frequency
varying between 300 and 500 cycles per second flows through its windings. In fact, the
movement of the telephone diaphragm is practically nil at 10,000 cycles per second, and
at frequencies of the order of one-half million per second, the telephone diaphragm cannot
keep pace with the reversals of flux. And even if it could, no sound would be heard,
because the human ear will not respond to vibrations in excess of 20,000 per second.
Another factor working in opposition to connecting the telephone in the antenna
circuit directly, is the fact that the impedance of the telephone winding will not permit
high frequency currents to pass. Hence we are compelled to either convert the current
of radio-frequency into a uni-directional pulsating current or into an alternating current
of a frequency within the range of the human ear.
Currents of radio-frequency induced in receiver aerials may be made audible by means
of a simple rectifier — a device which will permit the preponderance of current to flow
through a given circuit in one direction only. If a rectifier is placed in series with a circuit
132
PRACTICAL WIRELESS TELEGRAPHY.
A A A
RECTIFIED
CURRENT
/if\ A An
TELEPHONE
CURRENT
Fig. 148a, b,
-Showing how Incoming: Oscillations are converted to
Direct Current Pulses.
in which a current of radio-frequency is flowing, the latter will be converted into a direct
or pulsating current. Numerous minerals and compounded elements, notably among these
carborundum, have been found to possess the property of rectification, and hence a group of
incoming oscillations such as shown in Fig. 148a may have either their positive or negative
currents cut off as in Fig. 148b, and if a head telephone is connected in series with the rectifier,
pulsating direct current will traverse the windings as shown in Fig. 148c.
Now, if continuous
•K « * rAcr,, , *-r, J?c" oscillations of unvary-
ing amplitude were in-
duced in the receiver
aerial, the rectified
current would merely
displace the telephone
diaphragm and hold
it in this position until
the current is turned
off, but since in the
damped systems of
radiotelegraphy, the
oscillations are dis-
continuous, or occur
in groups, the current
falls to zero at the end
of each group, and,
hence, the diaphragm
of the telephone is re-
leased, creating a sin-
gle sound.
126. Simple Receiver. — The circuits of a simple radio receiver appear in
the diagram of Fig. 149, wherein a crystal rectifier D, connected in series with the
antenna A, is shunted by the receiving telephone P.
The action of this apparatus during the reception of signals may
be explained as follows : A train of waves radiated by the trans-
mitter induces an alternating current in the aerial circuit which
will flow freely through the crystal in one direction, but will be
opposed in the opposite direction. In one direction, let us say, the
current passes from the earth upward through the crystal, and thus
places a charge on the aerial wires, but the return current is op-
posed; hence the rectified oscillations (for each spark of the trans-
mitter) accumulate a charge on the antenna wires, which at the
termination of a wave train leaks to earth through the head tele-
phone, creating a single sound for each group of incoming
oscillations.
Because of its resistance, the crystal impedes the free flow of
oscillations and, therefore, to some extent, destroys the tuning
qualities of the aerial circuit. Hence, to enhance the tuning prop-
erties of the antenna system, the crystal is removed therefrom and
connected in a second circuit, termed the "local detector" circuit.
127. The Inductively Coupled Receiver. — The two
circuit receiver is shown in the diagram of Fig. 150, where-
in a coil L-l, connected in the antenna circuit, performs the
double function of adjusting the frequency of the antenna
system to resonance with the transmitter and transferring
the induced oscillations to a secondary circuit, consisting of
the coil L-2 shunted^ by the variable condenser C-2. More
clearly, the second circuit is coupled inductively to the first
circuit. A crystal rectifier, D, and head telephone, P, joined
Li
Fig. 149— Circuit of
Simple Radio Receiver.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
133
Fig. 150 — Fundamental Diagram of an Inductively
Coupled Receiver.
in series, are connected across the terminals of the secondary condenser. The two
circuits are distinguished in the following manner : The circuit comprising the aerial
and the primary winding of the receiving tuner L-\ is called the open oscillation
circuit, and the circuit comprising the
^ 7 secondary coil L-2 and the variable
Nlr , . , . condenser C-2, is called the closed
oscillation circuit. They are also
termed the primary and secondary cir-
cuits, respectively.
The current induced in the receiving
aerial is made audible in the receiving
telephone in the following manner : When
oscillations flow in the receiving aerial,
an alternating current passes through L-l
and a corresponding alternating magnetic
field cuts through the turns of L-2, induc-
ing therein a current of radio-frequency
which is built up in amplitude by placing
the two circuits in electrical resonance.
The variable condenser C-2 not only permits the closed circuit to be adjusted to resonance
with the open circuit, but also permits a closeness of adjustment which the usual secon-
dary inductance changing switch does not afford. If the coupling between the primary
and secondary windings is relatively
"loose," rather large amounts of capacity
and small amounts of inductance are em-
ployed in the closed circuit, for the best
strength of signal, but if the coupling be-
tween the windings is close, small values
of capacity and rather large values of in-
ductance are the factors which contribute
to the maximum strength of signal.
The oscillations built up in the sec-
ondary circuit by adjusting it to reso-
nance with the antenna circuit, overflow
to the shunt detector circuit, where part
of the current is rectified by the crystal
detector D and stored up in the con-
r> « OM. i. i ± j • Fig- 151— The Conductively Coupled Receiver.
denser C-l. Ihe charge accumulated in
the latter during the time of a single train of oscillations, discharges through the head
telephone P, causing the telephone diaphragm to vibrate at a rate corresponding to the
spark frequency of the transmitter.
128. Other Methods of Coupling. — Tf the open and closed oscillation cir-
i -i , J£P\. cu*ts °f a receiver are coupled through
\ / xQ (j. an auto-transformer as in Fig. 151, the
two circuits are then said to be di-
rectly or conductively coupled.
In this system part of the turns of a
single coil constitute the primary cir-
cuit and part the secondary circuit; the
turns bet-ween the points A and B may be
considered as the primary winding of the
tuner, while those from B to C may be
said to constitute the secondary winding.
Now the oscillation frequency of the an-
tenna circuit can be increased or decreased
by the variable contact A and similarly
Fig. 152— The Capacitively Coupled Receiver. f th d t t ' 't b t t C Fun
damentally the operation of this apparatus is similar to the inductively coupled receiver
with the exception that part of the current induced in the antenna circuit flows directly
through the shunt path afforded by the detector circuit. The disadvantage of this method
W
*
134
PRACTICAL WIRELESS TELEGRAPHY.
of coupling is that any change of wave-length adjustment of the open and closed circuits
changes the coupling, but this can be prevented by connecting an aerial tuning inductance
in series with the primary winding. The primary and secondary windings may be "loosely"
coupled at any particular wave length adjustment, by adding turns at the aerial tuning
inductance and taking them out at the primary winding. This will decrease the mutual
inductance of the two circuits and therefore will reduce the coupling.
The method termed the capacitive coupling is shown in the diagram of Fig. 152. The
primary and secondary coils shown at L-l and L-2 are not in direct inductive relation.
Pi B,
Fig. 153a, b, c — Complete Circuit for a Carborundum Rectifier and Receiving Tuner.
They are said to be electrostatically coupled through the condensers C-l and C-2. In
practice, the condensers C-l and C-2 are mounted on a single shaft and their capacity
varied simultaneously by a single control knob. It is claimed that since a fixed potential
exists across coil L-l the energy transferred to the secondary circuit varies as the capacity
of condensers C-l and C-2. Now the greater the coupling the greater will be the transfer
of energy from the antenna to the detector circuit and hence the coupling* between the
*The author has had practically no experience with the capacitive receiver and therefore cannot speak
authoritatively on -the working of this circuit.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
135
circuits varies as the capacity of the coupling condensers. It is claimed this circuit
possesses the advantage that a fixed degree of coupling between the primary and
secondary windings can be held while the wave length adjustment of the antenna and local
detector circuits is being varied throughout the range of the tuner. It is probable, however,
that this statement requires qualification.
In general the student will note from the foregoing that in any complete
wireless telegraph system four circuits must be adjusted to or tuned to the same
frequency of oscillation in order that communication may be established, as
follows: At the transmitting station the closed and open oscillation circuits are
adjusted for resonance. At* the receiving station the receiving aerial circuit is
adjusted to the frequency of the oscillations of the transmitter and the local or
secondary circuit adjusted to resonance ivith the receiving aerial circuit; and
for maximum response, the receiving detector must be adjusted to its maximum
state of sensitiveness.
129. The Carborundum Detector and Tuning Circuits. — The most widely
used of all detectors is the carborundum crystal rectifier, the tuning circuits for
which are shown in Fig. 153a, b, c. These diagrams indicate as well the apparatus
included in a modern receiving set. In addition two modified circuits showing
the connection of the potentiometer in various modern tuners, are presented.
Before proceeding with an explanation of the circuits of Fig. 153a, the function
of the potentiometer will be explained.
The application of a weak battery current to the carborundum crystal and head tele-
phone circuit has been found to have a marked effect on the intensity of the incoming
signals, but the strength of the current
must be carefully and closely regulated
and must be passed through the crystal in
a definite direction to secure the maximum
response. Ignoring for the moment an
explanation of the function of the local
current in a radio receiver, the reader
should note the diagram, Fig. 154, showing
the connections of the potentiometer to a
local battery.
A resistance coil A, D, is connected to
the terminals of a 2 or 4 volt battery B-l.
A shunt resistance R has the variable con-
nection B which is generally a sliding con-
tact. R may be taken to represent a car-
borundum rectifier. According to the law
of divided circuits, the maximum E. M. F.
is maintained across R when B is shifted
to the end D, but in the direction opposite or towards A, the E. M. F. gradually reduces
to zero.
In the circuit originally adopted for the carborundum crystal, the poten-
tiometer and detector were connected as in Fig. 153-a, but the modified circuits
of Fig. 153-b and Fig. 153-c are also in use. In Fig. 153-b the telephone and
potentiometer are shunted across the stopping condenser C-2 but in Fig. 153-c
the potentiometer is connected in series with the crystal rectifier. Since the
resistance of the crystal exceeds that of the potentiometer by several thousand
ohms, the resistance of the latter has little effect on the strength of the incoming
signal. Although practically equal results are obtained with either connection,
the circuit of Fig. 153-b is pointed out by some investigators to be the one which
gives the maximum response.
130. Adjustment of the Inductively Coupled Tuner. — During the reception
of wireless telegraph signals the inductive receiving tuner may be adjusted to
resonance with the sending station in the following manner :
If the secondary circuit is calibrated in wave lengths corresponding to various positions
of the secondary condenser and inductance switch, and a table of wave lengths supplied,
2 VOLTS
wwwvwwww
4 VOLTS
II
Fig. 154 — Connections of Potentiometer for Crystal
Detector.
136 PRACTICAL WIRELESS TELEGRAPHY.
the secondary circuit may be set directly to the wave length of the incoming signal, taking
care to select large values of inductance and small values of secondary capacity for any
particular wave. The secondary winding should then be placed in partial inductive relation
to the primary winding, followed by varying the capacity and inductance of the antenna
circuit until response is obtained. This is to be followed by adjusting the sliding contact
on the potentiometer and trying new points on the crystal rectifier until the loudest signals
are obtained in the head telephone.
Because the capacity and inductance of ships' aerials differ considerably it is evident
that a given primary winding will afford different wave length adjustments with different
aerials, consequently, the primary inductance changing switch cannot be calibrated directly
in wave lengths previous to installation. But after the receiver is installed, the primary
and secondary circuits both can be readily calibrated by comparison with a wavemeter
and the adjustment for any particular wave length quickly duplicated whenever required.
In event that a receiving tuner is not calibrated, the receiver can be tuned to a given
transmitter in the following manner:
(1) Set the secondary circuit approximately to the required wave length using
large values of inductance and small values of capacity;
(2) Place the secondary inductance in close inductive relation to the primary
inductance ;
(3) Add inductance in the antenna circuit until response is obtained in the
head telephones;
(4) Adjust detector to maximum degree of sensibility by potentiometer;
(5) Then reduce coupling between primary and secondary windings;
(6) Try new values of inductance and secondary condenser, also new values in
the aerial circuit;
(7) Adjust in this manner for maximum strength of signals or until interfer-
ence is eliminated.
(a) Theory of adjustment. Part of the energy of the oscillations induced in the receiver
aerial is lost by the resistance of the antenna conductors, part by re-radiation of the energy
in the form of a wave motion and the remainder through transference to the local detector
circuit. The energy imparted to the detector circuit is useful energy because it produces the
response in the head telephone, but the energy extracted in. this manner also has a marked
effect on the tuning qualities of the receiving antenna, which must be taken into account.
This may be explained as follows : If the secondary circuit is coupled loosely to the
primary circuit, small amounts of energy will be extracted from the antenna .oscillations ;
hence, the antenna will oscillate with greater persistence and will only respond with free-
dom to electric waves, the frequency of which coincides with its natural frequency of
oscillation. On the other hand, if the primary and secondary circuits are coupled closely,
a greater amount of energy will be extracted from the incoming oscillations and they will
therefore be damped out more rapidly than under conditions of close coupling. The re-
ceiving aerial will, under these conditions, respond to waves, the frequency of which may
be somewhat greater or less than the natural frequency of the aerial circuit.
Thus it is seen that if the two circuits are closely coupled, the receiver circuits will tune
"broadly" or if coupled loosely, the circuits will tune "sharply," that is to say, when the
receiving transformer coils are loosely coupled, a small change of inductance or capacity
will eliminate the signals of a given station, but when the receiver is "tightly'' coupled, a
much larger change of inductance or capacity will be required to eliminate the signals.
This can be stated in another way by saying that the change of coupling between the
primary and secondary circuits alters the effective resistance of the antenna and, therefore,
has direct influence on the damping of the antenna oscillations.
It has been shown by several investigators that maximum response is obtained in a
receiving apparatus so adjusted that the resistance of the primary and secondary circuits
are equal and since the effective resistance of any receiving system varies widely according
to the design of the aerial, the earth plate resistance and the type of receiving apparatus,
it is clear that some particular degree of coupling of the tuner will give the maximum
response in the head telephone.
The two circuit receiver with inductive coupling permits the receiving operator to
eliminate the signals from -interfering stations; in fact by judicious adjustment (of the
coupling) signals of the same wave length can be eliminated provided they have different
decrements. Generally an advancing wave of feeble decrement permits the primary and
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
137
secondary circuits to be loosely coupled and conversely a highly damped wave requires the
receiver circuits to be closely coupled.
The antenna circuit at any receiving station can be made to tune more sharply by
connecting a variable condenser in series and adding inductance until the wave length
adjustment for resonance is obtained. This decreases the natural decrement of the re-
ceiving aerial but generally results in decrease of the strength of signals but the loss of
signal strength is more than compensated for by the degree of selectivity obtained.
The sharpest tuning or the highest degree of selectivity is obtained in the local detector
circuit when the variable condenser in shunt to the secondary winding is worked at small
values of capacity with correspondingly large values of inductance for a given wave
length ; but if loose coupling is employed greater values of capacity and lesser values of
inductance may increase the selectivity.
As will be seen from the foregoing
0 explanations, interference can be prevented
\^ at the receiving station: (1) by employ-
^^^ ing loose coupling between the primary
I " ^^^» and secondary windings; (2) by inserting
a condenser in the antenna circuit and
adding inductance until resonance is se-
cured for a given wave length.
Irrespective of the selectivity obtained
by radio-frequency tuning, spark trans-
mitters having different spark notes tend
to prevent interference. By skill obtained
through practice, the receiving operator
can pick out a spark note of particular pitch and translate the signals through the inter-
ference of one or more stations, the more so if the spark note of the station desired has a
distinctive pitch. Occasionally interfering stations can be tuned out by detuning the closed
and open circuits, but signals will only be received in this way when the receiving station
is situated near to the transmitting station.
131. The Action of the Carborundum Crystal. — Before proceeding with an
explanation of various detectors and
the circuit best adapted to their
operation, we will briefly consider a
generally accepted explanation of the
operation of the carborundum de-
tector and the function of the local
battery current during the reception
of radio signals.
The student is now aware that if we
have a circuit such as shown in Fig.
154a, consisting of a variable source of
Fig. 154a — Circuit for Determining Volt-ampere
Characteristic of a Given Conductor.
6
VOLTS
155 — Characteristic Curve of Ordinary
sistance.
direct current B to which is connected a
resistance R and an ammeter A in series
and if the voltage at B is progressively
increased, the flow of current as indicated by the ammeter, increases in the direct ratio in
accordance with Ohm's law. Furthermore, if we plot the results of this experiment in the
form of a graph on cross section paper, as in Fig. 155, we find that a line drawn common to
all co-ordinate points located in accord-
ance with the data, will be straight and
f — }£J 1 uniform. Let it be noted from this, curve
^*k that if the voltage be doubled, the current
~"~^~~ is doubled and so on.
Now if we substitute for the resistance R
a crystal of carborundum D as in Fig. 156,
Twe find first, that the current in one direc-
tion with a given impressed voltage is
) much greater than when passed through
the crystal in the opposite direction and
second, that if the current flows in the
Fig. 156 — Apparatus for Determining Volt-ampere
Characteristic of Carborundum Rectifier*
*Diagrams Figs. 155 and 156 should have a voltmeter in shunt to the source of E. M. F. and a
regulating resistance in series.
138
PRACTICAL WIRELESS TELEGRAPHY.
direction of best conductivty and the voltage again progressively increased, the results do
not accord with Ohm's law as the curve, Fig. 157, clearly indicates, e. g., the current is not
proportional to the voltage. It will be seen that at first the current does not increase as
rapidly as it should to be in accord with Ohm's law and after a certain critical value of
voltage is passed the current exceeds the value to be expected by the same law. A curve
of this type is said to have a rising characteristic.
We may now assume this curve to apply to the detector circuit of Fig. 153a and that
signals are being received from a given station. Let the E. M. F. of the battery be three
volts. From the curve,
20 Fig. 157, we note that
the corresponding cur-
rent is 6 microamperes.
Now let the alternating
current of radio-fre-
quency (the incoming
signal) have for pur-
poses of illustration a
potential of one volt and
let it be superposed upon
the battery current flow-
ing through the crystal.
Then in one direction 1
volt will be added to 3
volts and from the
curve, the current corre-
sponding to 4 volts is
16 microamperes. But
when the alternating
E. M. F. flows in the
opposite direction it op-
poses the local battery
and the resultant E. M.
F. is 2 volts. Reading
from the curve we obtain
a current value of 2.5
microamperes.
It will thus be seen
under the influence of
the impressed alternat-
ing E. M. F. that the cur-
1234
VOLTS
Fig. 157 — Characteristic Curve of Carborundum Rectifier.
rent in the local battery circuit varies between 2.5 and 16 microamperes, but the sound
produced by the head telephone, as will be explained, is proportional to the difference between
the normal current flowing through the crystal and the average value of current flowing
when an external oscillating voltage is applied. This, perhaps, can be more clearly
explained by means of the curves shown in Fig. 157a, where the effect of superposing the
antenna oscillations on the local battery current over the duration of a single train of incom-
ing oscillations is shown.
As shown in Fig. 157, the normal current flowing through the head telephone, when no
oscillating voltage is applied, is 6 microamperes (the voltage of the battery being 3 volts),
but when an oscillating current of 1 volt is added on that of the local battery, the maximum
amplitude of the initial oscillation (Fig. 157a) in the wave train is 16 microamperes, and,
of course, successive maxima will be of lesser amplitude according to the decay of the
wave train (as shown by the series of decaying maxima). We see also that the suc-
cessive reductions of the normal battery current (shown below the line A, B) are rela-
tively small because, as shown in Fig. 157, for all voltages less than 3 volts the flow of
current (in microamperes) through the local circuit is relatively weak. The result of this
it seen to be a series of positive maxima of gradually decreasing amplitude to which
the telephone diaphragm cannot respond individually but which produce an average effect
in the receiver. The average current in the case of Fig. 157a may be considered for mere
illustration to be 9 microamperes and the difference between the normal current 6 micro-
amperes and the average current 9 microamperes (or 3.5 microamperes) is the current
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
139
which produces audible sound in the receiving telephone. We may state the foregoing in
another way by saying that the added voltage due to the oscillating E. M. F. being im-
C-D APPROXIMATE AVERAGE TELEPHONE. CURRENT
A- 6 NORMAL 6ATTERY CURRENT
BALL JOINT
Fig. 157a. — Curves Showing the Fluctuations of the Local Battery Current flowing
through the Carborundum Rectifier during the Reception of Signals.
pressed upon the crystal is greater than the subtracted voltage and that the final effect of
this is an increase of current through the head telephone circuit over the duration of one
wave train.
From the foregoing explanation
it is apparent that when an operator
at a given receiving station adjusts
the position of the sliding contact
on the potentiometer for maximum
signals, he adjusts the flow of cur-
rent through the crystal and head
telephone to correspond to the
critical point on the characteristic
curve, or, in other words, to that
point on the curve where the super-
position of a slight antenna E. M.
F. upon the local E. M. F. causes a
relatively large change in the
strength of the local battery cur-
rent. And it also follows that the
steeper the characteristic curve of
a given crystal, the greater will be
the change of current for a given
impressed alternating voltage. In
other words, the crystal with a
steep curve will give the loudest
signals and is said to be "more sen-
sitive" to incoming oscillations.
132. Adjustment of Crystal
Detectors. — No specific rule for lo-
cating the sensitive spot on a crystal
rectifier can be laid down; in fact, the
pressure and position of the opposing
contact for maximum signals can only
be determined by experiment. Car- Fig. 158— Carborundum Detector Complete.
CARBORUNDUM
/CRYSTAL
LSTEEL CONTACT POINT
140
PRACTICAL WIRELESS TELEGRAPHY.
BORNITE /ZINCITE
Fig. 159 — The Zincite Bornite Detector.
borundum crystals as a whole require greater pressure at the opposing contact than crystals
of galena, silicon, etc., although certain crystals under observation have required exceed-
ingly light contact pressure. With all crystals employing a local battery, it is important
that the local current flow in a certain direction and that its strength be carefully regulated.
This means in practice that either the connections to the battery must be reversed, or the
crystal must be turned about in the holder and left at the position in which the loudest
signals are obtained from a given sending station. The potentiometer, of course, must be
adjusted simultaneously.
The circuit of Fig. 153-b is suitable for the zincitc-bornite detector provided a fixed
resistance of about 2,000 ohms is connected in series with the battery B-l and the poten-
tiometer P-l. Certain crystals of this
combination respond better with a local
battery while others do not require it,
but with practically any crystal it aids at
least in obtaining the sensitive adjust-
ment to employ a local battery, e. g., the
sensitive spot can be more quickly
located.
If the test buzzer to be described
further on is employed, a crystal can be
adjusted to sensitiveness whether or not
the distant transmitter is in opera-
tion.
133. Detector Holders. — Two types of crystal holders appear in figs. 158
and 159. The first is suitable for the carborundum crystal which is mounted in a
small brass cup with some form of soft metal such as Wood's metal. A small
point, such as a steel phonograph needle, is mounted on the movable arm
and makes contact with the crystal. During adjustment this point is "jabbed in"
at various points on the crystal until a sensitive spot is located.
A detector holder suitable' for the zincite-bornite detector is shown in Fig. 159. The
large cup is filled with 5 or 6 zincite crystals while the opposite cup carries a crystal
of bornite. The cup is fastened to the end of the arm with the universal joint. The
crystal of bornite may thus be placed in
contact with the surface of any of the
zincite crystals being shifted from one to
the other until the adjustment for maxi-
mum strength of signals is found.
A variety of crystals holders have
been designed for crystals of galena, sili-
con, cerusite, etc. One type appears in
Fig. 160, where the crystal is held in a
small cup by three screws. A light wire
contact mounted on the movable arm
bears with slight pressure on the surface
of the crystal.
134. Classification of the Receiving Detectors. — The receiving detectors
of wireless telegraphy differ greatly both in point of mechanical construction ana
mode of operation, and, in addition, they possess widely varying degrees of sen-
sitiveness. Certain types, for instance, are highly sensitive to electrical oscilla-
tions but are difficult to keep in permanent adjustment; others are less sensitive
but possess marked degrees of stability. Still others are in the nature of a com-
promise and may occupy approximately a position midway between the two
extremes.
Some receiving detectors rely upon the principal of rectification (as we have
already shown) and will convert an alternating current of radio-frequency to a
uni-directional current; others have the property of rectification combined with
the ability to vary a local source of battery current in a manner much similar to
the working of an ordinary telegraph relay. The operation of certain other detec-
tors is based upon the influence of electrical oscillations upon magnetised iron or
Fig. 160 — Detector Holder for Galena and Silicon
Crystals.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS. 141
upon the ability of these Oscillations to cause certain granulated metals to cohere.
Perhaps the most highly developed of all receiving detectors are the vacuum
tube rectifiers which are extremely sensitive and possess the important property
of amplifying the signals when connected in cascade. Certain types of vacuum
amplifiers will remain in a sensitive state of adjustment over an indefinite period
or throughout their length of life.
It should be kept in mind that the most sensitive receiving detector is not always the
one most convenient or the most practical for commercial use. For instance, extremely
-sensitive amplifying detectors may require intricate apparatus, having so many points of
adjustment that its manipulation may call for the services of a highly skilled engineer and
further the circuits may be of such a type that the apparatus cannot be quickly changed
from one wave length to another. In event of the latter, the tuner would be of little value
for marine service which requires the receiver to be one capable of quick adjustment
to land stations operating at various wave lengths. Furthermore, extremely sensitive de-
tectors bring in a certain amount of interference from far distant stations which would not
be heard on less sensitive detectors.
The most practical detector for commercial working is one that combines a fair degree
of sensibility with ruggedness and stability" of adjustment, and so far among the crystal
detectors none has, in this respect, excelled the carborundum rectifier. The Marconi mag-
netic detector is universally recognized as being the most stable and "foolproof" of all re-
ceivers but it lacks sensitiveness on the shorter waves. The vacuum valve detectors, on
the other hand, are considered to be the most sensitive among commercial receivers, but
they possess the disadvantage of requiring complicated circuits for best results.
To impress upon the reader's mind the utility of the various types of receiving
detectors, we may classify them under five general headings. Under the first
heading we may name the detectors which require no local battery and under the
second heading, those detectors in which the response in the telephone depends
upon the application of a local battery current as well as upon the current of the
incoming oscillations.* Certain detectors may be classified under both headings
because they may function to some extent with or without a local battery.
In addition we may note under a third heading the detectors considered as
rectifiers of radio-frequent currents and in a fourth and fifth headings, those
suitable for response to either damped or undamped oscillations respectively. It
is to be noted that a few types come under all headings.
Detectors Functioning f Galena-Silicon-Zmcite Bornite-Carborundum (sat-
Without Local Battery I lsfactory for short distance receiving)— Fleming Valve
(_ (filament battery only).
Detectors which depend C
upon the combined effects of I Carborundum— Zincite Bornite (sometimes used with
received energy and local ] local battery)— Fleming Valve (with local battery)—
battery current. [ Three Element Valve— Silicon.
f Galena — Silicon — Carborundum — Cerusite — Zincite-
%££?** Va,ve-Three Element Valve-
{Galena — Silicon — Zincite Bornite — Carborundum
— Fleming Valve — Three Element Valve — Marconi
Magnetic-(Tikker, Tone Wheel and Heterodyne sys-
tem will give some response from spark transmitters,
but are not satisfactory for such reception).
Detectors of Undamped f Tikker — Tone Wheel — Heterodyne Receiver — Vacuum
Oscillation. \ Valve Oscillator.
135. Fleming Valve Detector and Tuning Circuits. — A receiving detector
of notable merit is the Fleming oscillation valve the action of which is primarily
*Footnote: We should be careful to distinguish between detectors requiring a "local battery" and
those requiring a local "source of energy." For example, the Tikker, the Tone Wheel and the Marconi
Magnetic detectors require a local driving force, which in reality take the place of the local battery; also
the Heterodyne receiver requires a local source of radio-frequent currents upon which the response in the
receiver depends as well as the current induced in the receiver aerial.
142
PRACTICAL WIRELESS TELEGRAPHY.
based on the emission of electrons from highly heated metals in vacua. In its
commercial form it consists of a highly exhausted glass bulb, Fig. 161, containing
a 4 or 12 volt lamp filament, F, of carbon, platinum or tungsten surrounded by a
metal plate or cylinder P-2 of copper, nickel, etc., from which a connection is
extended to the outside of the bulb.
When the filament is brought to a state of incandescence by a battery B, negative
electricity can pass from the filament to the plate, but not in the opposite direction, hence
when the terminals of the
closed or secondary cir-
cuit of a receiving tuner
are connected to the nega-
tive side of the filament
and to the plate of the
valve, the alternating cur-
rent of radio-frequency
flowing in the receiver
circuits will be converted
into a uni-directional cur-
rent which may affect a
head telephone or other
recording instrument.
More clearly, the oscilla-
tions flowing in the re-
Fig. 161 — Fleming Oscillation Valve and Tuning Circuits.
ceiver circuits during the time of a complete group will be rectified by the valve placing a
charge in the condenser C-2 (Fig. 161), which afterwards discharges through the head
telephone, creating a single sound for each group.
The adjustment of the Fleming oscillation valve i-s extremely simple and the stability of
the device particularly marked, in fact it is only necessary to adjust the incandescence of
the filament until loud response from a given station is obtained in the head telephones.
This is accomplished by the rheostat R which normally is of 10 or 15 ohms resistance.
Fig:. 162— Fundamental Circuit of Marconi Valve Tuner.
The Fleming valve gives signals of greatest strength when the secondary
circuit is designed for a minimum value of shunt capacity and a maximum value
of inductance for a given wave length or frequency, hence the secondary con-
denser is always worked at low values of capacity.
Many valves are more sensitive if an added potential is applied between the filament
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
143
and the plate. Like the carborundum detector, the Fleming valve has a rising char-
acteristic and when an E. M. F. is applied to the space between the plate and the fila-
ment the current may be adjusted to the critical point on the characteristic curve so that
the addition of a slight antenna voltage causes a large increase of the local battery current
flowing through the head telephones.
A satisfactory diagram appears in Fig. 162 wherein a potentiometer P-l is
shunted across the filament battery and a portion of the current flows through
the head telephones and the detector. With this arrangement of circuits ad-
vantage is taken of the particular volt-ampere characteristic of the valve and a
relay action due to a local source of energy is obtained. For the maximum
strength of signals with this circuit it is necessary to adjust the position of the
sliding contact on the potentiometer as well as the incandescence of the filament,
until the desired results are obtained.
The diagram, Fig. 162, shows the fundamental circuit of the widely used
Marconi-Fleming valve receiver. The open circuit comprises :
(1) The aerial tuning inductance L-l,
(2) The short wave condenser C-l,
(3) The primary winding L-2,
(4) The shunt impedance R-l,
(5) The change-over switch S-l, S-2, S-3.
The intermediate circuit comprises :
(1) The winding L-3 in inductive relation to L-2,
(2) The winding L-4 in inductive relation to L-5,
(3) The variable condenser C-2.
The secondary circuit comprises :
(1) The secondary winding L-5,
(2) The billi condenser C-3,
(3) The Fleming valve F, P,
(4) The battery B (or four volts generally),
(5) The 10 ohm rheostat R.
(6) The 400 ohm potentiometer P-l,
(7) The fixed condenser C-4,
(8) The head telephone P-l.
Inductances L-2, L-3, L-4, L-5, L-6 are of fixed value, but L-l is variable through
the medium of a multi-point switch.
When the D. T. three blade switch S-l is
thrown to the right, primary winding L-2 is
connected in series with the aerial circuit
which brings the intermediate circuit into use,
but the switch, thrown in the opposite direc-
tion, disconnects L-2 and connects L-6 in
series with the aerial. L-6 being wound
tightly about the turns of L-5, the open and
closed circuits are closely coupled. This in-
creases the damping of the receiving system
and makes the set responsive to waves of dif-
ferent length at one set of adjustments, but,
of course, does not give the strength of sig-
nals that can be obtained by resonant adjust-
ments.
The position of the switch corresponding
to "close coupling" is marked "Stdbi," an ab-
breviation for the word "standby." The switch
is placed in this position when a particular
receiving station awaits a call from one of
several sending stations which are not exactly
tuned to the same wave length.
In the opposite position, the changeover
... >, 1 -^ L\ • -a. Fig. 1&3 — Carborundum Crystal Holder to Fit
switch is marked tune and with the circuits Fleming Valve Socket
CRY5TAL
TENSION
ADJU5TOR
CONTACT
POINT
VALVE
SOCKET
144
PRACTICAL WIRELESS TELEGRAPHY.
of this connection, sharp resonant adjustments can be obtained. The wave length of the
intermediate circuit is increased or decreased by the variable condenser C-2 only and simi-
larly the wave length of the secondary or detector circuit, by the condenser C-3.
The coupling between the inductances of the intermediate circuit and inductively related
coils is varied simultaneously by means of a shaft (and knob) upon which both coils, L-3
and L-4, are mounted.
The impedance coil R-l prevents the accumulation of high voltages upon the dielectric
of the variable condenser, which may be punctured in case the windings of the tuner should
come in direct contact with the high voltage wires of the transmitting apparatus.
The American Marconi Company has developed a crystal holder to fit in the
Fleming valve socket as shown in Fig. 163. The circuit for the crystal detector
is practically identical with that of the oscillation valve with the exception that
the lighting battery is connected to the potentiometer instead of to the lamp
filament.
- ELEMENTAL Y-
- DIAGRAM OF CONNECTIONS —
- 107-A TUNER -
EXTERNAL CRYSTAL
Fig. 164 — Complete Circuits of Type 107a Tuner (American Marconi Company).
The valve tuner was original designed to be responsive to waves varying be-
tween 300 and 1 ,650 meters in length, but the circuit has been modified to respond
to waves up to 2,500 meters, as in Fig. 164.
136. Marconi Type 107-a Tuner. (American Marconi Company). — The
various connections and arrangements of circuits of the Marconi type 107-a
tuner are shown in Figs. 165-a, 165-b and 165-c. The principal change over the
ordinary valve circuit lies in the special six point double throw switch (marked
"change-over switch") which disconnects the condenser of large capacity (.01
microfarads) across the intermediate circuit and places it in shunt to the second-
ary winding and the billi- condenser (see Fig. 165-a). With the increased capacity
of this condenser in shunt, the secondary circuit will respond to a wider range
of wave lengths than the original design of the tuner would permit.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
145
For the reception of wave lengths exceeding 1,500 meters, the D. P. D. T.
switch is thrown to the "standby** position and the intermediate circuit cut out.
For wave lengths below 1,000 meters, either the "standby" or "tune" circuits can
be employed at the discretion of the operator.
It is to be noted, although the 107-a tuner is designed for the carborundum
detector, an extra set of posts is provided for an additional crystal such as
Fig. 165a — "Standby" Long Wave Adjustment of Marconi Type 107a Tuner.
cerusite. When the latter detector is employed, the potentiometer is out of the
circuit. Observance next should be made of the binding posts from which wires
are connected to the receiver circuits and to the contacts of an aerial change-over
switch. The latter, when open, protect the detector and head telephones from the
induced potentials of the local transmitter.
Fig. 165b — "Tune" Circuits of Type 107a Tuner.
In the diagram, Fig. 165-b, L-l is the aerial tuning inductance, the value of which is
altered by means of a multi-point switch mounted on the left hand front of the tuner.
C-l is the short wave variable condenser connected in series with the aerial system. In
the full scale position it short circuits itself and is thus cut out of the antenna circuit. This
condenser is mounted on the left hand side on the top of the tuner.
L-2 is the primary winding of the receiving tuner and has a fixed value of inductance
(not variable).
146
PRACTICAL WIRELESS TELEGRAPHY.
Coil L-3, condenser C-2, coil L-4 comprise the intermediate circuit. L-3 is of fixed value
and is in inductive relation to L-2. L-4 has the same dimensions as L-3, but it is in in-
ductive relation to coil L-5.
The wave length of this circuit is varied by means of a condenser C-2.
i-S
C-J
C-4
Fig. 165c— "Standby" Short Wave Circuits of 107a Tuner.
Coils L-3 and L-4 are wound on balls or spheres, mounted on a shaft so they can be
turned at a right angle to L-2 and L-5, simultaneously. This is effected by means of the
coupling knob mounted on the right hand end of the tuner, and thus the coupling between
the intermediate circuit and the antenna and detector circuits is varied as required.
&U.U
*' CONDENS
Fig. 166— Type 107a Tuner (Modified Valve Tuner).
Coil L-5 and condenser C-3 constitute the secondary circuit. L-5 is of fixed value and
C-3 is the well known "billi" condenser, having a value of about .0001 microfarad.
C-4 is the telephone condenser of approximately .003 microfarad capacity.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS. 147
R is a sliding contact potentiometer of 400 ohms, mounted on the left hand side of the
tuning box.
B is a dry cell battery of 1.5 to 3 volts, while D is the usual carborundum crystal.
The inductance coil, L-7, is an inductive static leak for preventing the accumulation of
large static charges upon the plates of the short wave variable condenser to prevent the
rubber dielectric from puncturing.
During adjustment of the carborundum crystal, the connection from the battery to the
potentiometer must be reversed until the best response is obtained.
The intermediate circuit of either of the foregoing tuners is employed in case of ex-
cessive interference from nearby stations. Of course it is difficult to distinguish between
stations operating on the same wave length except as the signals from the desired station
are very much louder than those from the interfering station ; but transmitters operating on
the same wave length and having different degrees of damping can often be tuned out or
in by proper adjustment of the coupling.
It will be apparent from the preceding diagrams that either the valve or the 107a tuner
is tuned to resonance with the incoming signal by condensers only, with the exception of
the aerial tuning inductance which is
variable in steps through a multipoint
switch. A photograph of the 107a tuner
appears in Fig. 166. In adjusting this
tuner, the following general instructions
should be observed:
(a) Operation. With the connection
("Tune") indicated in Fig. 165b the tun-
ing is extremely sharp and the circuits
will not respond to wave lengths in excess
of 1,000 meters.
For general work the coupling knob is
set at 90°. The billi condenser is set at
the zero position on the scale and one or
two points of the aerial tuning inductance
connected in the circuit. The setting of
the intermediate condenser, C-2, is altered
until response is secured.
Correct setting for the potentiometer is Fig 166a_Marconi Disc Variable Condenser.
obtained by means of a buzzer tester or
by listening to the signals of a distant station. Follow this by reversing the connections
from the battery to the tuner until the loudest signals are obtained.
For tuning to waves up to 1,000 meters, three or four points of inductance should be
added at the aerial tuning inductance, but for the wave lengths shorter than 600 meters, the
short wave condenser should be used at smaller values of capacity.
The billi condenser permits the detector circuit to be tuned to waves from 450 meters to
1,000 meters in length.
(b) "Stand-by" Position. When the double throw knife blade switch is thrown to the
left — "stand-by" position — the circuits are altered as in Fig. 165c. With this connection the
primary winding L-2 is disconnected from the antenna circuit and a second primary wind-
ing, L-6 connected instead.
L-6 is an inductance of fixed value wound tightly around the winding L-5, giving a
close degree of coupling between the aerial and detector circiuts.
From the diagram it will be plain that coil L-4 of the intermediate circuit is still in
inductive relation to L-5 and unless the precaution is taken to turn the coupling knob to the
zero position, considerable energy will be absorbed from the detector circuit, thereby re-
ducing the strength of the incoming signals, particularly if the intermediate circuit is in
resonance with the antenna and the detector circuits.
For tuning to waves up to approximately 1,000 meters with the "Stdbi" connection, only
the billi condenser is employed in shunt to the secondary winding, but for longer wave
lengths the small six-point, double throw switch, mounted on the top of the tuner (marked
change-over switch in Fig. 164), is placed in the "Stdbi long wave" position, whereupon the
intermediate condenser, C-2, is connected in shunt to the billi condenser C-3. This connec-
tion permits waves in excess of 3,000 meters to be adjusted to in the secondary circuit.
148 PRACTICAL WIRELESS TELEGRAPHY.
The complete circuit for this connection is indicated in Fig. 165a. Note carefully that
the intermediate circuit is not employed. It is important to note also that the type 107-a
tuner is fitted with four binding posts (at the rear) from which connections extend to the
type S aerial changeover switch. When the antenna switch is placed in the transmitting
position, the circuits of the 107-a tuner are interrupted at the points A and B (Fig. 165b),
thus breaking the circuit to the detector and the head telephones. The contacts at this
switch must have careful inspection from time to time, for, unless they close properly, the
apparatus positively will not function.
Should these contacts be broken, a permanent jumper should be placed across the bind-
ing posts to keep the circuit closed.
Type 107-a tuner should be used with the type S or type I aerial changeover switches
only.
The complete circuits for the tuner are shown in detail in Fig. 165a and with the fore-
going explanation, the functions of the various elements should be clear without further
instruction.
(c) General Instructions. For "stand-by" tuning or broad adjustment at wave lengths
up to 1,000 meters (see Fig. 165c), place the double throw knife switch to the left.
Set the condenser switch on "tune."
Set the coupling knob at zero. Carefully
adjust the billi condenser. Connect in a
few points of the aerial tuning inductance.
Vary the capacity of the short wave con-
denser.
For long wave lengths (in excess of
1,000 meters) place the condenser switch
on "stand-by long wave" position. Vary
carefully the capacity of the intermediate
condenser. Add inductance at the aerial
tuning inductance.
For sharp tuning on the shorter wave
lengths (below 1,000 meters), place the
double throw knife switch to the "tune" position. Place the condenser switch on the "tune"
position. Set the coupling knob at from 70° to 90°. Adjust carefully the intermediate con-
denser. Add two or three points of inductance at the aerial tuning inductance. Follow
this by variation of the capacity of the short wave condenser. In this position, all the
variable elements of the complete tuner are in use.
137. Marconi Magnetic Detector and the Multiple Tuner Circuits (Eng-
lish Marconi Company). — The magnetic detector shown diagrammatically in
Fig. 167 is an oscillation detector of unvarying stability. A description of the
detector and an explanation of its functioning follow :
A continuous band made up of a group of fine iron wires revolves on the ebony
grooved wheels W which are turned by clockwork in the base of the instrument. The
band passes through the glass tube G, which has a small single layer of fine wire comprising
6 to 10 turns through which the radio-frequent oscillations flow. Directly over this wind-
ing is placed the small bobbin of wire S which has approximately the resistance of the
head telephones P-l. Two horseshoe permanent magnets with like poles adjacent are
mounted immediately above the tube and near to it. Some argument exists concerning the
action of this detector during the reception of signals but it is sufficient to say that when
the iron band passes underneath the two permanent magnets it undergoes a cyclic change
in magnetism and is extremely sensitive to an impressed external magnetic field such as
that generated by a radio-frequent current flowing through the winding G.
When electrical oscillations induced in a receiver aerial by a distant transmitter pass
through the winding P, one complete group of oscillations sets up an alternating magnetic
field which causes a single movement or a change in the position of the flux in the iron
band. The bobbin S being in the path of the flux, it is acted upon inductively, a current
being induced in the windings which flows through the head telephone creating a single
sound for each group of incoming oscillations. The note of the transmitter is faithfully
reproduced, because each group of oscillations radiated by the transmitter has a cumulative
effect on the change of flux in the iron band, which creates a single movement of the tele-
phone diaphragm. Although the magnetic detector lacks the sensitiveness of the crystal
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
149
detector throughout the shorter range of wave lengths, as between 300 and 600 meters,
for waves around 2,500 meters, it compares favorably with the most sensitive crystal
rectifiers.
The magnetic detector may be connected directly in series with the aerial
system, but it func-
tions best in the
circuits of the Mar-
coni Multiple Tun-
er (English Mar-
coni Company) in
Figs. 168 and 169.
In general, the
circuits of this
tuner appear simi-
lar to that of the
valve tuner, but the
secondary winding
for the magnetic
detector has very
few turns as compared with the secondary of the valve tuner. The magnetic
detector has low resistance compared with crystal detectors and, in consequence,
the stopping condenser of the usual detector circuit becomes an active element of
the closed oscillation circuit and must therefore be of variable capacity. In fact,
placing the detector in series with the secondary circuit not only calls for a wind-
ing of low inductance but one of low resistance as well. Hence the secondary coil
is usually wound with rather coarse wire, such as No. 18 or No. 20 B. and S.
Fig. 167a — Marconi Multiple Tuner.
C»- C, IN SERIES
A = 80 TO ISO METEFW Cs • Ct
I C* C,
C- IN SERIES WITH AERIAL
C, ACROSS INTERMEDIATE CIRCUIT
C « IN SEWES WITH MAGNETIC DETECTOR.
Ibb — fundamental Circuit Marconi's Multiple Tuner.
A fundamental wiring diagram of the Marconi multiple tuner appears in Fig. 168 and a
more detailed diagram showing approximately the position of the apparatus in the tuner
in Fig. 169. Like notations are used in both drawings.
Since this tuner is adjustable to wave lengths between 80 and approximately 3,000
meters, a specially constructed series of multi-point switches S-l, S-2 and S-3 (Fig- 169)
control the inductance and capacity of the primary, intermediate and secondary circuits for
a progressive increase or decrease in wave length. The particular wave length adjustment
corresponding to any position of the switch is clearly marked on the operating handle.
150
PRACTICAL WIRELESS TELEGRAPHY.
When the small D. P. D. T. switch is placed in the "standby" position, the magnetic
detector is connected directly in series with the aerial and the necessary tuning adjustments
are made at inductance L-l and condenser C-l, but when this switch is thrown to the
'"tune" position, the aerial circuit continues through the primary winding L-2, the oscilla-
tions being transferred from thereon to the intermediate coil L-3, built up in amplitude by
condenser C-2 and finally transferred to L-5 by induction from L-4.
The function of the switches S-l, S-2 and S-3 will be clear from the drawings and the
following explanation, describing the connections of the various fixed and variable capaci-
ties for the complete range of wave lengths.
MAGNETIC DETECTOR
Fig. 169 — Detailed Wiring Diagram of Multiple Tuner.
For wave lengths from 80
to 150 meters.
For wave lengths from 150
to 600 meters.
For wave lengths from
1,600 to 2,000 meters.
For wave lengths from
2,000 to 2,600 meters.
Condensers C-4 and C-l are in series.
Condensers C-5 and C-2 are in series.
Condensers C-6 and C-3 are in series.
Condenser C-l is in series with the antenna.
Condenser C-2 is in shunt to the intermediate circuit.
Condenser C-3 is in series with the magnetic detector.
Condenser C-l may be in or out of the aerial circuit as
required.
Condenser C-7 is in shunt to condenser C-2.
Condenser C-8 is in shunt to condenser C-3.
Condenser C-l is in or out as required.
Condensers C-9 and C-7 are in shunt to condenser C-2.
Condensers C-10 and C-8 are in shunt to condenser C-3.
The switch S-l in the foregoing drawings selects such values of inductance at L-2 as
will give the correct degree of coupling at all wave lengths. The protective leak inductance
R prevents the accumulation of heavy charges in the condenser C-l. The coupling be-
tween L-2 and L-3, and L-5 and L-4, is varied simultaneously by a single knob on the side
of the box. A protective gap R protects the primary circuit of the tuner should by accident
the circuits come in contact with the high voltage wires .of the transmitter.
Because of the small secondary winding, this tuner is not suitable in the "tune" position
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
151
for a crystal detector, but will give some response on the "standby" side in which connec-
tion the crystal is connected in series with the aerial.
It has frequently been observed that the magnetic detector gives better response to 500
cycle transmitters when the iron band revolves at a speed about twice that used in receiving
from 60 cycle transmitters. Normally the band travels at a very low speed — a few feet per
minute.
Fig. 170 — Type 106 Receiving. Tuner (American Marconi Company,).
138. The Marconi Type 106 Receiving Tuner. (American Marconi Com-
pany).— A receiving set of particular excellence combining mechanical and
electrical features of merit is the type 106 tuner of the American Marconi Com-
pany. This set is of the panel type, the necessary controlling switches being
mounted on the front of the board as shown in photograph 170, the coupler,
variable condensers, potentiometer, etc., being mounted on the rear as in photo-
graph 171. The coupling between the primary and secondary windings is varied
by means of a special rack and pinion adjustment which is in turn controlled by
a knob on the front of the panel with a scale marked from zero to 10 (marked
"coupling").
The inductance of the primary winding is changed by means of two multi-
point switches, one of which operating in conjunction with a barrel switch discon-
nects the unused portions of the primary winding for any particular adjustment
of wave length. That is, the primary tvinding is divided into four groups which
are cut into the circuit as the wave length is progressively increased. The con-
nections to the separate aerial tuning inductance connected in series with the
antenna system are included in the "tens" switch of the primary winding. The
"unit" switch controls 10 single turns of the primary winding permitting any
number of turns from one to maximum to be included in the circuit (as will be
explained in paragraph 191).
The aerial circuit includes a short wave variable condenser which in the 180°
position short circuits itself automatically by means of special contacts fitted to
the movable and stationary plates. The secondary coil divided into 10 groups
152
PRACTICAL WIRELESS TELEGRAPHY.
is fitted with an end-turn switch which splits the winding into three complete
groups. The secondary winding is shunted by a variable condenser which in the
zero position is completely disconnected from the circuit, thereby cutting off the
Fig. 171— Rear View Type 106 Receiving Tuner.
capacity effect between the opposite plates (of the variable condenser) in the
so-called zero position of capacity.
A special wire wound potentiometer is supplied, having a resistance of about
450 ohms, the value of which is adjusted by a rotary multipoint switch.
The receiving de-
lector, placed in a ver-
SHORT WAVE VARIABLE
T
TESTER
1/2 — -Fundamental Circuit Diagiam 106 Tuner.
front of the panel,
consists of a contact
point with spring-
pressure mounted on
a universal joint
which may be placed
in contact with the
sensitive spot on one
of several crystals
mounted in a cup di-
rectly underneath.
A fundamental dia-
gram of the type 106
tuner is shown in Fig.
172, which, as will be
observed, is somewhat
similar to the connec-
tions of Fig. 1531x
The part of this dia-
ticular attention is the
connection of the
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS. 153
potentiometer, the head telephones and the fixed condenser C-3, and the group-
ing of the primary and secondary turns. The buzzer excitation system shown
will be described in detail in paragraph 149.
The reader should note that the 106 tuner is constructed so that only the used turns of
the primary and secondary windings are in direct inductive relation, that is, the unused
turns of either winding do not overlap and consequently when the primary and secondary
are set at low values of inductance, care must be taken to have these two windings in the
correct inductive relation. For instance, by a little consideration, it will be evident that if
the secondary winding is placed too far inside the primary coil the coupling is decreased just
as it is when the secondary winding is drawn out of the coil.
The general instructions for the adjustment of the inductive receiving tuner given in
paragraph 130 are thoroughly applicable to the type 106 tuner. An increase of inductance
in the antenna circuit for adjustment to a given wave length should be followed by an
increase of the secondary inductance to maintain resonance. Also with each change of
wave length there is a critical degree of coupling which gives the louder signals in the
head telephone.
Under conditions of loose coupling the secondary variable condenser is of some use
to reduce interference, but under conditions of close coupling the condenser is preferably
set near to zero values of capacity.
The short wave variable condenser is employed to tune the antenna circuit to signals the
wave length of which is below the natural wave length of the receiving antenna. Response
to shorter waves is obtained at capacities near to the zero position of the condenser scale.
With this condenser in circuit, the wave length of the antenna system will be progressively
increased (that is, the oscillation frequency decreased) as the control handle is moved in the
direction of maximum capacity. In case of severe interference, the damping of the receiv-
ing antenna may be decreased in the following manner: For a given wave length set the
short wave variable condenser at a certain value of capacity and obtain resonance by
adding inductance at the aerial tuning inductance until maximum ' response is obtained.
Care must be taken to select the correct values of inductance and capacity, which, of
course, vary with each aerial. If excessive values of inductance are added, variation of
capacity will have little effect on the incoming signals. The fact is that signals would not
be heard under these conditions unless the transmitting station is near to the receiving
station. Correct values of inductance and capacity are assured if a slight change in con-
denser capacity eliminates the signals.
G
Fig. 173 — Type 101 Receiving Tuner (American Marconi Company).
We may resume the function of the elements of the tuner as follows: The small push
button marked "Test" immediately to the right hand side of the receiving tuner closes the
circuit from the battery to the buzzer which permits the manipulator to obtain the best
adjustment of the crystal. When turned to the right this button is locked in position. The
two switches on the front of the Type 106 tuner marked "transformer primary" vary the
inductance of the primary circuit. The switch marked "Units" cuts in a single turn at a
time. The switch marked "Tens" varies the primary inductance in groups of ten turns at
each point of contact.
154 PRACTICAL WIRELESS TELEGRAPHY.
The primary condenser has minimum capacity in the zero position but if turned to the
180° mark it is shunted by a special set of contacts (attached to the movable plates and
thus cut out of the aerial circuit. All control handles attached to the inductance changing
switches and variable condensers of the primary and secondary circuits should be turned
counter clockwise for increase of their values.
r
Fig. 174 — Rear View Type 101 Receiving Tuner (American Marconi Company).
The switch marked "transformer secondary" and the control handle marked "secondary
condenser" control the inductance and capacity of the secondary circuit. The wave length
adjustment of the circuit can be increased by turning the switch or the knob of the con-
denser counter clockwise. Different values of inductance and capacity can be employed in
this circuit while holding the same wave length. This changes the damping of the circuit
and proper proportioning (of inductance and capacity) may give increased strength of
signals during the reception of signals from certain stations.
The control handle marked "potentiometer" varies the flow of current through the de-
tector crystal. Close adjustment of the potentiometer is necessary when the incoming
signals are comparatively weak. The switch marked "battery" turns the local battery cur-
rent on and off.
The terminals marked "battery" connect to four dry cells in a separate box and the
terminals marked "telephones" are the binding posts for connection to 2,000 ohm receivers.
As the transmitter operates at approximately the wave length to which the secondary
circuit of the receiver is adjusted, it produces exceedingly strong signals which are liable
to impair the sensitive condition of the crystal. To obviate this, connections are made with
the antenna switch so that when the antenna switch is in the transmitting position the
terminals of the detector and the secondary condenser are short-circuited. Care should be
taken to see that the antenna switch, with which this receiver is to be used, is so con-
structed as to perform the above operations. If this is done, the transmitter has very little
or no effect on the sensitiveness of the crystal and it will, therefore, be in a sensitive
condition for receiving immediately after transmission. (See diagrams, Figs. 201, 202
and 203.) In addition to paragraph 130 the student should read the general instructions
in paragraph 156a.
139. Marconi Receiving Tuner Type 101 (American Marconi Company). —
The type 101 receiver consists of an inductively coupled transformer with two
solid rectifier detectors and the necessary accessory apparatus mounted on a hard
rubber panel and enclosed in a mahogany case. The front elevation of this set
is shown in photograph, Fig. 173, the rear elevation in Fig. 174, and a funda-
mental diagram in Fig. 175.
The aerial is connected to the binding post "antenna" and the earth connection is made
to the binding post marked "ground." The circuit between these two points is adjusted to
resonance with the incoming signal by variation of the two transformer primary switches,
the primary loading coil switch, the primary condenser, and the primary condenser switch
which is marked "out" "series" and "shunt." The purpose of this switch is to connect the
primary condenser in series or in parallel to the aerial or to disconnect the condenser
entirely.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
155
Thus for long wave lengths the condenser is placed in shunt to the primary winding
and for waves below the fundamental period of the aerial the condenser is thrown in
series with the primary winding.
The function of the three other primary switches is to vary the number of turns of
inductance in the aerial circuit.
The secondary circuit contains the transformer secondary coil, the inductance of which
is varied by the transformer secondary switch, the secondary condenser, the* cerusite and
the carborundum detectors, the switch for connecting either of these two in the circuit,
the potentiometer, and the switch marked "sent," "receive."
ANTENA
B
175 — Fundamental Diagram Type 101 Tuner.
The transformer secondary is moved in or out of the transformer primary coil by
means of the handle marked "coupling." The capacity of the secondary condenser is
varied by rotation of its handle, and the potential across the carborundum detector is
varied by the rotation of the potentiometer handle.
Supplied with this set is a mahogany box containing four dry cells having three binding
posts, marked 1, 2, and 3. Nos. 1 and 2 connect to the two binding posts on the receiver
immediately under the word "battery," while No. 3 is connected to the post at the extreme
right on the same level with "test" switch. This post completes the circuit from the battery
to the test tuner.
Since the detectors work better with the battery current flowing in a certain direction,
it is necessary to determine experimentally which binding post to connect to the carbon
and which to the zinc electrode.
The head telephones are connected to the binding post "telephones." The binding posts
marked "antenna switch A," posts 1 and 2, and "antenna switch B and C," posts 1, 2, and 3,
are for connection to a specially designed navy type antenna switch.
When the navy switch is not used, posts Al and A2, B2 and B3, Cl and C2, and B3 and
Bl are short circuited with pieces of thick copper wire.
The posts marked "extra detector" are for connection with an outside detector. If the
outside detector requires battery, place the detector switch in the position marked "car-
borundum," if not place it in position marked "cerusite."
The test buzzer is mounted within the metal cup directly over the secondary condenser
and can be adjusted if necessary by removing the two cap screws.
Since the satisfactory operation of the set depends to a great extent on the switch
blades making perfect connection with the switch studs, it is necessary to see that there
is always good firm pressure between them. If for any reason this pressure becomes too
weak, remove the screw in the handle, take off the handle, and remove the two screws
156
PRACTICAL WIRELESS TELEGRAPHY.
holding the switch blades in place. The blades can then be bent slightly so that when
replaced they will make positive contact.
The complete adjustment of this tuner is as follows: Set the primary condenser switch
to position "Out," place coupling pointer at about 7 on the scale, detector switch to "ceru-
site," secondary condenser pointer to position "Out," potentiometer to O, "send" and "re-
ceive" switch to "receive" (if used with navy switch or break system relay, leave in "send"
position always), turn test switch to "In" position, which starts the buzzer; then adjust
Cerusite Detector point on crystal surface until loudest response is heard. This crystal
requires very light pressure for maximum sensitiveness and the point may be screwed up
or down by turning the hard rubber knob to left or right.
Having found a sensitive point in the crystal, vary the inductance of the two primary
Fig. 176 — Wiring Diagram Marconi Universal Receiver.
transformer switches until the desired signal is heard, then loosen the coupling by rotating
coupling handle to the right until the signal is just audible, then try other points of trans-
former secondary switch and rotate secondary condenser handle to the left until a com-
bination is found which gives maximum response.
The primary should then be readjusted more accurately until the best setting is found
and the coupling then adjusted until the maximum strength of signal is obtained. The
longer the wave length the greater the number of turns of inductance necessary in primary
and secondary circuits. If more inductance is necessary for a particular signal and cannot
be obtained by adjustment of transformer primary switch, place this in position marked
"Out" and rotate the primary loading coil switch from its position "Out" until sufficient
turns are in the circuit.
If the wave length of the incoming signal is shorter than can be reached with primary
condenser switch in the "Out" position, place it in the series position, set the ten turn trans-
former primary switch at zero, the unit .turn transformer primary switch at 10 and rotate
primary condenser handle until maximum response is obtained.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
157
Placing the primary condenser switch in the "Shunt" position increases the wave
length of the aerial circuit corresponding to any given setting of the inductance switches.
This may be done at any time instead of increasing the inductance. Generally speaking, the
method of varying inductance is preferable and gives a louder response, but in exceptional
cases the reverse is true and in any particular case a trial of the two methods can be made
to find out which is the better. The best secondary setting for maximum response to any
particular wave length is that of maximum inductance and minimum capacity, but the
greatest selectivity will be obtained with smaller inductance and greater capacity.
When the carborundum detector is in use it will be necessary to adjust the potentiometer
to a point which gives the greatest sensitiveness.
It should be noted that when using the Cerusite detector during the reception of very
weak signals the potentiometer should always be in zero position, but for signals of mod-
erate intensity it does not matter particularly what position this may happen to be in. In
order that the operator may be able to measure approximately the wave length of the
incoming signals, calibrations of the secondary are given with each tuner, it being under-
stood that these are correct only when the secondary is coupled very loosely to the primary.
With the 101 receiver are supplied adjustable head telephones which are tuned to the
group frequency of the transmitter. Also the electrical circuit through the telephones and
the stopping condenser is tuned to the same group frequency.
It is advisable occasionally to insert a piece of paper between the spark points of the
antenna and ground binding posts and telephone binding posts to make sure they are not
short-circuited.
140. The Marconi Universal Receiving Set (English Marconi Company).—
The complete circuits
of the Universal Crys-
tal Receiver are indi-
cated in the diagram.
Fig. 176, and a photo-
graph of the finished
instrument in Fig.
177, the tuner having
been designed for
wave lengths between
300 and 3,000 meters.
The circuits are ap-
plicable to all types of
crystal rectifiers, par-
ticularly those of car-
borundum, z i n c i t e,
bornite, etc.
The usual aerial tun-
ing inductance is represented at L-l, the short wave condenser at C-l, and the primary
winding of the tuning transformer at L-2. L-2 has three tappings, which are varied by
means of the switch. The secondary circuit of the receiving tuner is divided into three
units, the following range of wave lengths being obtained with each: L-3 has the correct
values for all wave lengths up to 600 meters; L-4 for waves between 600 and 1,600 meters,
and L-5 for waves between 1,000 and 3,000 meters. The necessary change of inductance is
obtained by the wave length changing switch D, which completely disconnects the unused
turns from the circuit.
The functioning of the switch is as follows : In one position the switch blade D is
connected to the high potential end of winding L-5 through contact point A ; but a longer
wave length adjustment is obtained by placing the switch on point B, which connects the
receiving detector to the high potential end of L-4, and at the same time the lower right
hand contacts alongside the switch spring together, joining the high potential end of L-3
to the low potential end of L-4. The same function is performed by switch point C and
the upper right hand set of contacts.
The secondary condenser shown at C-3 possesses at maximum very low capacity. The
potentiometer P-2 is shunted across the battery B-2. A protective choke is indicated at
P-4 and a safety gap at R. The telephone condenser C-2 is of fixed capacity.
A novel feature of this tuner is the magnets M-l and M-2, which are joined to battery
Fig. 177 — Universal Crystal Receiver (English Mai
>any).
158
PRACTICAL WIRELESS TELEGRAPHY.
178— Showing
Construction
Detector.
of Electrolytic
B-l, the terminals X and X-l extending to. a small switch alongside the transmitting key.
Closing this switch energizes the magnets, which draw the contacts on either side of the
crystal apart, completely disconnecting all attached circuits and thereby protecting the
detector from induction of the transmitter.
The magnets and the crystal holder are
mounted in a metallic box.
A number of vessels in the trans-
Atlantic service of the Marconi Com-
pany are fitted with this apparatus
which has been found to permit recep-
tion over very long distances.
141. Electrolytic Detector.— A
detector widely used in the early stages
of wireless telegraph development in
the United States is the so-called
"zvhisker point" electrolytic, which is
particularly sensitive and uniformly
stable in operation. Of late, however,
the electrolytic cell has fallen into
almost complete disuse for commercial
working, even though its reliability is
generally admitted. From a commer-
cial standpoint this may be accounted for by the fact that the initial adjustment
of the device is rather troublesome.
The essentials of the detector appear in Fig. 178, where a small glass receptacle R has
sealed in the base a small piece of platinum P about ^2-inch square. About a half-dozen
drops of a 20 per cent, solution of nitric acid or a supersaturated solution of caustic potash
cover the lower electrode. The upper electrode P-l is an extremely fine platinum wire
about .0001 inches in diameter. The depth of immersion in the liquid is carefully regulated
by a finely threaded screw adjustment. The platinum wire is generally coated with silver,
which afterward is dissolved by dipping the point of the wire in a strong solution of nitric
acid, leaving the small platinum tip exposed.
The silver need not necessarily be taken off the platinum wire by a strong acid solution ;
the point can be immersed in the usual detector solution of dilute nitric acid and an extra
strong local current sent through the cell for a few moments until the silver is completely
dissolved. Afterward the point is adjusted to just touch the solution.
Now, if this detector is substituted for the carborundum rectifier in the circuit of Fig.
153a, and the positive pole of the local battery connected to the fine wire electrode, the de-
vice becomes a very sensitive detector of currents of radio frequency, provided the small
electrode just touches the surface of the acid.
The fine wire electrode is frequently coated with glass, so that the extreme tip only is
exposed to the action of the solution, hence the depth of immersion of the entire electrode
is of little importance and the detector is less difficult to adjust.
Several theories have been advanced to account for the action of the electrolytic de-
tector, one being that the response in the local head telephone is caused by change in re-
sistance of the small platinum wire during the passage of radio-frequent currents.
Another investigator contends that the current of the local battery flowing through the
electrolytic cell forms gas bubbles which polarize the fine wire electrode, and thereby par-
tially reduce the flow of current from the local battery. Then when oscillations of radio-
frequency pass through the cell, the gas bubbles are temporarily destroyed, which permits
an increase of the strength of the local battery current at rates corresponding to the spark
frequency of the transmitter.
The electrolytic detector is adjusted for maximum strength of signals, by carefully regu-
lating the strength of the local battery current. If the current is too strong, a hissing sound
is obtained in the head telephone which will prevent the reception of signals. If, on the
other hand, the local current is too weak, the detector will barely respond. Some difference
of opinion exists regarding the direction in which the local current must flow through the
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
159
cell, but it is usual to connect the fine wire electrode to the positive pole of the cell.
H. Shoemaker has discovered that the large electrode may be of zinc, and if the small
platinum point and zinc are immersed in a dilute sulphuric acid solution, the cell not only
acts as a detector of oscillations, but supplies its own local E. M. F. as well. In this form
the detector is termed a primary cell detector.
142. The Three Element Valve Detector.— A modified type of the two
element Fleming valve is the three element valve, the circuits for which are shown
in Fig. 179. From the viewpoint of mechanical construction, it is practically
identical with the Fleming valve, with the exception that a metallic element known
as a grid is placed in the path of the electrons flowing from the filament to the
plate.
This grid may be made up of a zig-zag shaped platinum ^vire or a plate per-
forated with holes, or in certain types of valves it consists of a spiral of copper.
The filament may be constructed of tungsten, tantulum or platinum.
^ — •— -I The circuit generally
\ / adopted .for the three
\/ element valve appears in
Fig. 179, where the pri-
mary and secondary cir-
cuits of a receiving tuner
are represented by the
usual notations and the
grid, plate and filament
of the valve by G, P, and
F, respectively. An im-
portant part of this cir-
cuit is the so-called grid
condenser C-l, which
generally has low capa-
city, varying between
.00003 and .0005 micro-
farads.
In addition to the
lighting battery B-l,
which is generally of 4
volts, a local battery
B-2 of 35 to 200 volts
has its positive terminal
connected to the plate P and the negative terminal to the telephones P-l, which are in turn
attached to the positive end of the battery B-l. The secondary terminals of the receiving
tuner are connected to the negative terminal of the filament and to the grid.
In this form of valve as in that already described, the incandescent filament produces
electrons which give to the vacuous space conductivity in one direction only. In the two
element bulb, the plate element serves both to impress the received oscillations on the
vacuous space and to connect the telephone thereto. In the three element bulb these func-
tions are separated, the first being assigned to the grid and the second to the plate. A
gain in flexibility and ease of manipulation is thereby secured.
As in the two element valve, the electrons carry the local battery current as well as the
incoming oscillations and the effect of the latter is to vary the local battery current, pro-
ducing the so-called relay action.
According to the explanation advanced by Armstrong, the grid clement, if placed in the
path of the electrons, receives a negative charge which decreases the local battery current,
i. e., the current flowing between the plate and filament. An external positive charge applied
to the grid will in a degree neutralize the negative charge and thus increase the local bat-
tery current, but an external negative charge will cause greater absorption of electrons and
reduce the battery current to a lower figure. Hence, if an alternating E. M. F. be impressed
between the grid and filament the positive alternation increases the local battery current
and the negative alternation decreases it.
In order to receive the maximum strength of signals from spark stations, the detector
must be connected in a circuit that will permit an accumulative effect for each group of
Fig. 179 — Fundamental Circuit
for the
Valve.
Three Element Oscillation
160
PRACTICAL WIRELESS TELEGRAPHY.
POTENTIAL Of
GRID TO
FILAMENT
WING
CURRENT
TELEPHONE
CURRENT^
incoming oscillations. Such a circuit is shown in Fig. 179, which, according to Armstrong,
functions as follows : The radio-frequent oscillations induced in the secondary circuit of
the receiver are rectified by the valve action between the grid and filament, and a negative
charge is placed in the condenser C-l which, at the termination of a wave train, leaks off
the grid, exerting a relay action on the local battery current, decreasing its strength at
audio-frequent rates. At the termination of a group of incoming oscillations, the grid
returns to normal poten-
tial and also the local
current, whereupon the
process is repeated. If
the valve is properly con-
structed, i. e., if a good
sample is used, it is a
very sensitive detector,
much stronger signals
being obtained than
with an ordinary crystal
rectifier.
Oscillograms of this
detector taken by the
same investigator indi-
cate that the three ele-
ment valve not only func-
tions in the manner just
explained, but that the
oscillations of radio-fre-
quency flowing through
the grid circuit are re-
peated in the head tele-
phone circuit and super-
imposed upon the local
Fig. 180 — Curve Showing the Process by which the Three Element Valve u_ff._ TT
makes Damped Oscillations Audible. battery current. How-
ever, the radio-frequent
oscillations (repeated in the local battery circuit) do not affect the telephone diaphragm,
but the audio frequency variation of the continuous current in that circuit does create an
audible sound of a pitch determined by the spark frequency of the transmitting station.
The process involved in the detection of oscillations induced in the receiver
by a distant transmitting station can be shown by the curves of Fig. 180, which
indicate first : the oscillations of the incoming signals; second, the potential of
the grid circuit with respect to the filament; third, the decrease of the wing cur-
rent and the superposed oscillations of
radio-frequency, and finally, the result-
ing fluctuation of current in the head
telephone.
Either the current of radio- or
audio-frequency reproduced in the lo-
cal circuit of the vacuum valve can be
increased in amplitude by special con-
nections on the same valve or by con-
necting a number of valves in cascade.
In the first method, the current of
radio- or audio-frequency is repeated
back to the grid circuit by special
radio- or audio-frequency transform-
ers, but in the second method, a trans-
former is connected in the local battery circuit and its secondary terminals con-
nected to the grid and filament of a second valve by which the incoming radio signal
is amplified by repetition of the action shown in Fig. 180.
Fig. 181 — "Repeater" or "Regenerative" Vacuum
Valve Circuit.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
161
The three element vacuum valve connected in a simple tuning circuit for the reception
of spark signals is adjusted for the maximum strength of signals as follows: (1) The
incandescence of the lamp filament is carefully adjusted by the filament rheostat; (2) The
voltage of the local battery is varied until the maximum strength of signals is obtained.
To protect the filament and assist adjustment, modern sets have a small ammeter connected
in series with the lamp filament by which the degree of incandescence is definitely fixed.
143. A Repeater Vacuum Valve Circuit. — A method for repeating the
current of radio frequency flowing in the telephone circuit back to the grid circuit
of the same bulb appears in Fig. 181. This system has been found to be particularly
successful in operation and gives increased strength of signals from a given sta-
tion. Part of the energy of the oscillations of radio-frequency flowing in the
telephone circuit is repeated back to the secondary circuit through the coupling
coils (of radio- frequency) L-l and L-2, and the amplitude of the grid oscillations
thereby increased. The amplified grid oscillations then react upon the telephone
circuit, producing still greater variation of the local current, thus further reinforc-
ing the oscillations of the system.
Fig. 182 — Audio-Frequency Repeater Circuit. Fig. 183 — Tuned Regenerative Vacuum Valve Circuit.
The complete process does not interfere with the action of the valve as a detector,
which at the same time charges the grid condenser in the usual fashion, but with in-
creased strength, due to the repeating action of the system.
To permit the oscillations of radio-frequency to flow across the telephones, the con-
denser C-3 is connected in shunt. This circuit will function without the condenser C-3,
the necessary capacity being found in the parallel cords of the telephone.
The current of audio-frequency flowing in the local telephone circuit may be repeated
to the grid circuit by the method shown in the diagram of connections, Fig. 182, where
a coil of audio-frequency (one of large inductance values) L-l is coupled inductively
to a similar coil, L-2, which is connected in series with the secondary winding of the
receiving tuner. C-2 permits the oscillations of radio-frequency to pass to the grid and
filament and also serves to tune the circuit L-2, C-4 to the audio-frequent current of the
local circuit. Although in this case an audio-frequent current is also dealt with, the action
is identically the same as in repeating back currents of radio-frequency.
A circuit has been evolved by Armstrong where both the radio- and audio-
frequent currents can be simultaneously repeated back to the grid circuit and
although considerable amplification of the incoming signals is thus obtained, the
system has been found difficult to keep in stable operation.
Referring again to the circuit diagram, Fig. 181 (where the current of radio-frequency
in the local telephone circuit is repeated back to the grid circuit) , an improvement can
be effected by the connections shown in the diagram, Fig. 183, where the local circuit
is tuned to resonance with the grid or secondary circuit by the tuning coil L-4. The
condenser C-3 shunts the head telephone and battery, while the coil L-l repeats the
oscillations of radio-frequency back to the grid circuit through the coil L-2. The circuit
is suitable for the reception of damped or undamped oscillations, and has been found to
magnify the incoming signal several hundred times.
162
PRACTICAL WIRELESS TELEGRAPHY.
It will be noted from the foregoing diagrams, Figs. 179 to 183, and the explanations given,
that three principal circuits, which may be termed the primary, secondary and tertiary cir-
cuits, must be placed in resonance, the tertiary circuit being the local telephone circuit, with
its tuning coils and condensers. The
three circuits are not only adjusted (in
the case of the reception of spark signals)
to substantial resonance, but in addition
the coupling of the repeating transformer
must be carefully adjusted, as well as the
coupling between the primary and secon-
dary windings. Correct values of induc-
tance and capacity must be selected in each
of the three circuits for any particular
wave length. Beyond the tuning of the
third circuit, the general mode of opera-
tion is practically the same as with the
ordinary radio-frequency tuners,
rig. 184 — Simple Regenerative Circuit. T , ,, . , . ,
It should not require explanation that
with the amplification of signals obtained by the circuits shown in Figs. 179 to 183 the useful
range of transmitting apparatus has been considerably increased.
Another circuit for the amplification of incoming radio signals is shown in the diagram,
Fig. 184, wherein the principal point to be observed is the connection of the secondary
terminals of the receiving tuner to the vacuum valve.
One terminal is connected through the grid condenser to the grid and the opposite ter-
VALVE 1
VALVE 2
VALVE 5
Li L-Z Ls L4
Fig. 185 — Vacuum Valves Connected in Cascade.
minal to the plate of the valve instead of to the filament. The local battery B-2 and the
head telephone P, are shunted by a condenser C-3, and an additional condenser C-4 is
connected between the grid and filament of the valve. The mode of operation of this circuit
probably does not differ from the repeating circuits previously described, because, as will
be seen, there is a certain amount of electrostatic and magnetic coupling between the second-
ary and tertiary (local telephone circuit)
circuits. The system is adjusted in the fol-
lowing manner : The secondary circuit, in-
cluding the secondary condenser, is tuned
to resonance with the primary circuit and
the incoming wave. The condenser C-l is
set at very low values of capacity, and
the capacity of C-3 varied, also C-4, until
maximum response in the head telephone
circuit is obtained. Like ordinary vacuum
valve circuits, the potential of the
battery B-2 must be carefully regulated
and the valve worked below the charac-
teristic "blue glow" point. The vacuum
• PHONES i
Fig. 186 — Cascade Connection of Vacuum Valve with
One Lighting Battery.
valve connected in this manner is suitable for the reception of either damped or undamped
oscillations.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
163
144. The Vacuum Valve Amplifier.- — The incoming signals made audible
by the simple vacuum valve circuit shown in Fig. .179, may be amplified consider-
ably by connecting several oscillation valves in cascade as per the diagram, Fig.
185. The fluctuations of current in the local circuit are impressed upon the grids
of a second and third valve where due to the relaying or trigger action of the bulb,
progressive amplification is obtained.
Fig. 187 — Circuit for Cascade Amplification of Radio Freqtu
In the diagram, Fig. 185, in which the left-hand part of the circuit starts with the sec-
ondary winding of the receiving transformer, the telephones are removed from the local
battery circuit and replaced by an iron core inductively coupled transformer of audio-fre-
quency dimensions. The primary winding L-l is connected in series with the battery B-2,
but the terminals jpf the secondary winding L-2 are connected to the grid and filament of
the second vacuum valve. The circuit continues in this manner throughout several bulbs,
but generally the fluctuations of current in the third or fourth step are strong enough to
paralyze the valve, particularly if the vacuum is not sufficiently good. Usually this
system does not function well above the third step. To prevent the accumulations of extra
high potentials on the grids of the amplifying valves, an extremely high resistance, R (of
from 500,000 to 1,500,000 ohms resistance) may be connected from the grid to the filament.
It is, of course, understood that the incandescence of the filament of each vacuum valve will
be carefully regulated by a small rheostat and the voltage of the local battery regulated until
the best operating condition for the individual bulb is obtained.
If the diagram of connections, Fig. 186, are adopted, a single storage battery may be
employed to light all valve filaments. It will be noted that the secondary circuit of the
audio-frequency transformer L-2, L-3 is conductively open, and although it is somewhat'
difficult to explain exactly how this transformer functions, good results are reported to be
obtained by means of it. Either of the foregoing types of amplifiers may be used to step
up the signals of an ordinary wire telephone as well as the signals of wireless telegraphy.
145. Amplification of Radio Frequencies. — By means of a cascade connec-
tion of vacuum valves, we may amplify the oscillations of radio frequency, trans-
ferring them from one bulb to another until the desired increase of signal is ob-
tained. A satisfactory diagram of connections appears in Fig. 187.
The circuits of radio-frequency are similar to that of any receiver, with the exception
that a small value of potential from a local battery is applied to the filament and grid of
each vacuum valve, the E. M. F. being adjusted by the potentiometers P-l and P-2. The in-
coming oscillations amplified by the first vacuum valve are transferred into the second
vacuum valve through the radio-frequency transformer L-5, L-6. The circuit of L-5 is tuned
to resonance with the incoming oscillations by the condenser C-5 and the secondary circuit
L-6, C-6 tuned to the same frequency by means of C-6. By proper adjustment of the volt-
ampere characteristic of the second bulb (by the potentiometer P-2) the effect of the in-
coming oscillations is to place a charge in the condenser C-7 in shunt to the head telephones,
164
PRACTICAL WIRELESS TELEGRAPHY.
which in turn discharges through the windings of the telephones, causing a single sound.f
More in detail, by proper adjustment of the potentiometer in the grid circuit of the last
valve, the amplitude of the positive half of the radio-frequent current repeated in the
tertiary or local telephone circuit exceeds the amplitude of the negative half, and, due to
this fact, more current flows in one direction than in the other; accordingly, the telephone
condenser C-7 becomes charged over a period corresponding approximately to that of the
duration of a wave train and then probably discharges in one direction through the head
telephones at rates corresponding to the spark frequency of the transmitter.*
146. The Effects of Distributed Capacity. — Every coil of wire possesses a
certain amount of distributed capacity (sometimes termed self -capacity), e. g.,
energy is stored up between adjacent turns during the flow of oscillations in the
form of electrostatic lines of force, which produce an effect similar to connecting
a small condenser in shunt to the coil.
Thus a tuning coil of given dimensions, having considerable self -capacity, will have a
_ — __ 1. i - . defined time period of oscillation and will
CD
CD
Fig. 188 — Showing the
"Dead-end" or "End"
Turns of a Receiver Tun-
ing Coil.
Fig. 189 — Showing the
Position of an End Turn
Switch.
respond more freely to one impressed
frequency than to another. Now, it is
found by experiment that a crystal de-
tector, such as the carborundum rectifier,
gives the loudest response in the receiv-
ing telephone when the maximum possi-
ble voltage for a given group of incoming
oscillations is impressed upon it, and gen-
erally a secondary receiver circuit in
which inductance predominates gives the
maximum possible voltage. Then if a
secondary circuit minus a shunt condenser
is constructed so that its natural oscilla-
tion frequency accords with the frequency
of the oscillations flowing in the trans-
mitter aerial, maximum response is se-
cured. All this may be summed up by
saying that a secondary receiver circuit
similar to one in which it is supplied, the
A primary winding having
lacking a shunt variable condenser functions
necessary capacity being found in the self-capacity of the coil,
distributed capacity is somewhat objectionable for use in tuning circuits, because an appre-
ciable amount of current will oscillate through the unused turns, particularly if the fre-
quency of the incoming signal equals the natural frequency of the coil. Coils made of fine
wire or those wound irregularly tend to reduce the effects of distributed capacity.
147. The End Turns of a Receiving Tuner and End Turn Switches. —
In the preceding paragraph the effect of distributed capacity in the windings of a tuning coil
was discussed, and the fact mentioned that a coil of given dimensions may have a well-defined
time period of oscillation and may therefore oscillate more freely to an impressed current of
a particular frequency.
Assume that such a coil is connected in series with the antenna circuit shown in Fig. 188
and that for resonant adjustment to the wave length of 600 meters the turns between points
A and B only are required. The remaining turns from B to C are therefore useless for
this particular wave length, and should the coil have a natural time period of oscillation
corresponding to the wave of 600 meters, an appreciable amount of current would oscillate
backward and forward through the unused or end turns. This in effect amounts to placing
a secondary circuit in resonance with the antenna circuit and results in the absorption of
some of the energy of the oscillations.
If the antenna system were only to be tuned to the maximum wave length of 600 meters,
the additional turns on the coil B to C would not be required, but inasmuch as the aerial
system may have to be tuned to various wave lengths up to 3,000 or 4,000 meters, the full
number of turns are required for the winding.
If then, for example, the coil A, C, is interrupted at the point D, E, as shown in Fig. 189,
the unused turns of the winding are conductively disconnected from the used turns and
t Note also the radio-frequency amplifier described in paragraph 226. Note also diagram Fig. 296.
* Explanation according to Armstrong.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
165
therefore a considerable amount of current which heretofore oscillated through the unused
turns is now converted to a more useful purpose.
All this leads to the point that the maximum diegree of efficiency and selectivity is
obtained from a receiving tuner having properly located "end turn" switches fitted to the
primary and secondary coils. It should,
however, be remembered that merely dis-
connecting the unused turns does not
completely prevent the absorption of
energy by that part of the circuit, but it
tends to reduce the absorption to a
minimum.
An "end-turn" switch may take one of
several designs but the fundamental con-
struction of the type used in the latest
tuners manufactured by the American
Marconi Company is shown in the dia-
gram, Fig. 190, where the successive groups
of a primary or secondary tuning coil are
represented at 1, 2, 3 and 4. Mounted
on a hard rubber drum are the copper
segments S-2, S-3 and S-4, which are
slightly offset so that the successive
units of the tuner winding are connected
in the circuit when the knob is turned
counter clockwise. The circuit is com-
pleted by brushes A and B which make
TAPS FOR STUD5 UNDER BLADE 5 . contact with segments S-2 and brushes C
Fig. 190— Sketch Showing the Construction of "End and D which make contact with S-3 and)
so on. In addition the switch blade S-l
makes contact with the taps of a multipoint switch (n.ot shown) which cuts in groups, 10
turns at a time. For example, when the switch S-l has been turned, let us say, counter
clockwise until all the turns of section No. 1 are cut into the circuit then segment S-4 makes
contact with brushes E and F, connecting section No. 2 in the circuit. The blade of the
multipoint switch S-l then progresses across the contacts connected to the turns of section 2
and when the last stud has been passed, the circuit is completed through the next group by
brushes C, D, which make contact with segments S-3. The switch blade S-l then pro-
gressively cuts in the additional turns of section No. 3 and so on until S-2 cuts in group
No. 4.
In the design of a commercial re-
\ceiving tuner, the primary or second-
ary winding is interrupted at points
suitable to the standard wave lengths.
For example, if sections 1, 2, 3 and 4
are the secondary units of a receiving
tuner, the winding is interrupted be-
tween 1 and 2 at such a point that the
wave length of the closed circuit
(with small values of capacity in
shunt) will be slightly above 600
meters. The next interruption of the
circuit will be made at a point where
the wave length adjustment is slightly
above 1,000 meters, the next for 2,500
Fig. 191 — Showing How the Inductance of the Radio
Frequency Tuning Coil Can Be Varied by
One Turn at a Time.
meters, and so on. The foregoing selections are those agreeable to American
practice where ships communicate with naval or Marconi ship and shore stations.
148. The Variation of a Radio Frequency Inductance. — In the earlier
types of receiving tuners, the inductance of the radio-frequency coils was varied
by mounting a sliding contact on a brass rod, the contact passing over successive
turns of bare wire. It is obvious that such a design is mechanically incorrect be-
166
PRACTICAL WIRELESS TELEGRAPHY.
O
cause the gliding contact soon cuts through the wire either actually breaking the
turns or short circuiting adjacent turns.
By the method shown in the diagram, Fig. 191, the inductance of a single layered coil
can be progressively varied from one turn to the maximum number simply through the
use of two multipoint switches doing away with the sliding contact.
For purposes of illustration, assume a winding having 110 turns. Then the first 10 single
turns are connected to the contact points of the switch S-2 and the remaining turns are
connected in groups of 10 to the contact points of the switch S-l. An odd number of turns
can be selected in the following manner :
If 87 turns are required for resonance in
any particular circuit, switch S-l is set
at the eighth contact point and switch
S-2 on contact point 80, making 87 com-
plete turns. One turn of inductance, for
instance, can be selected by setting S-l
at zero and S-2 at contact point 1. This
is the method by which the inductance
of the primary winding of the Marconi
type 106 receiving is varied.
It is not usual to vary the inductance
of the secondary circuit of a receiving
tuner in this manner. The method gen-
erally employed is to vary the inductance
by groups of 10 or 15 turns at a time,
the necessary closeness of adjustment
between groups being obtained by the shunt
variable condenser for sharp tuning.^
Extremely close variation of the
inductance of a radio-frequency cir-
cuit can be obtained by the instru-
rig. 192 — 1 he Construction of the Variometer. , , •'. ,,
ment termed the variometer, the
principle of which has already been explained in connection with the transmitter.
A variometer* suitable for receiving apparatus is shown in Figs. 192 and 193, where a
stationary coil A has mounted within it a ball winding B which rotates on a metal shaft.
A knob and pointer is attached to the shaft
and a suitable scale supplied. The ball
windings A and B are connected in series
and if, in one concentric position, they are
connected so that their magnetic fields op-
pose the inductance of the variometer will
be practically zero, but if the inner ball is
turned on its axis, the inductance will
gradually increase, maximum inductance
being obtained, when the inner coil has
completely changed sides with respect to
the outer coil. For receiving apparatus, the
inner and outer balls are generally wound
with No. 24 B. and S. wire if connected in
the antenna circuit and with No. 32 B. and
S. wire, if connected in series with the
secondary or detector circuit.
Although the variometer is a very
useful instrument for tuning the re-
ceiver, it possesses the disadvantage
of offering considerable resistance to
the passage of radio-frequent cur-
rents when used at inductance values
near to zero. That is to say, a sim-
' BINDING POST
POINTER
SCME
'Fig. 193 — The Tuning Variometer Complete.
*See paragraph 30; also fig. 18.
fSee section H appendix.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
167
Fig. 194 — Buzzer Excitation System.
pie tuning coil of the sarrie value of inductance, would obviously possess less
resistance.
149. Buzzer Excitation Systems. — If any part of an active vibrating buzzer
(energized by a battery) is placed in inductive relation to either the open or closed
circuits of a receiving set, the fluctuations of the battery current act inductively
on the receiving circuits and set up therein feeble currents which are rectified and
made audible in the head telephone.
Maximum response in the head telephone is obtained when the crystal rectifier
is adjusted for the best degree of rectification, hence the buzzer affords a ready
means for readjustment of a receiv-
ing detector of any type. A perfect
reproduction of the tone of the buzzer
is obtained in the head telephones, the
pitch varying in accordance with the
interruptions of the vibrator.
In one method a wire is extended
from some part of the buzzer circuit,
preferably the contact points, and is con-
nected directly to either the earth lead of
the receiving tuner or to one terminal of
the secondary circuit, but the better
method is to place some part of the cir-
cuit leading to the buzzer in inductive
relation to the antenna system as in the
diagram, Fig. 194. In this diagram a
small coil L-2 of 6 or 7 turns of wire
(about lJ/2 inches in diameter) connected
in series with the antenna system has
wound around it, 7 turns comprising the
coil L-l. Coil L-l is in series with the battery and the buzzer, and consequently when the
buzzer is set into action, a change of flux takes place through L-l which sets up a difference
of potential across L-2 and, therefore, charges the antenna system, causing it to oscillate at
the particular frequency to which it is adjusted. Then, when the secondary circuit of the
receiving tuner is adjusted to resonance with the antenna circuit and the crystal detector
adjusted for the most sensitive operating condition, the louder sound will be obtained in
the head telephone.
With supersensitive receiving apparatus it is sometimes necessary to place the buzzer
excitation circuit several feet from the windings of the receiving tuner to prevent the sound
in the head telephone from becoming of un-
bearable intensity.
Although various means have been devised
to shield crystalline detectors from the local
transmitting apparatus at a given station, none
have as yet afforded the desired protection.
Hence, it is generally necessary at the close of
a period of transmission to readjust the re-
ceiving detector to -its maximum degree of
sensitiveness. If the receiving tuner is fitted
with a test buzzer the detector can be quickly
readjusted by setting the buzzer into action and
changing the position of the opposing contact
to the crystal until the loudest signals are ob-
tained.
The ordinary vibrating buzzer can be
put to a variety of uses in radio telegraph
systems, such as exciting the circuits of a
wavemeter or setting up oscillations in an aerial system for radio telegraph meas-
urements. Such circuits will be described in the chapter following.
150. Receiving Telephones. — The flux generated by a given electromagnet
Fig.
194a— 3,000-Ohm Head Telephone
Receiver.
168
PRACTICAL WIRELESS TELEGRAPHY.
-B-
is determined by the product obtained in multiplying the strength of the current
by the number of turns, e. g., the ampere turns determine the magnetizing flux.
Hence, if a feeble current only is available, a magnet wound with a large number
of turns of fine wire will generate the greatest magnetizing flux.
Now the local circuit of the average telephone receiver, such as shown in Fig. 194a,
is traversed by feeble currents, and therefore the magnets of the telephones should
be wound with a great number of turns of rather fine wire such as No. 36 or No. 40
B. and S. Such a winding necessarily has considerable resistance, but a greater magnetizing
force will result therefrom than would be ob-
tained by a winding of a few turns of coarser
wire. The resistance of the average telephone
receiver for reception of radio signals is 2,000
to 3,000 ohms. These receivers are generally
more sensitive than the type employed in land
line telephony; but it should be borne in mind
that it is not alone the magnetizing flux gen-
erated that determines the volume of sound
produced by the telephone, but the overall con-
struction influences its sensitiveness as well.
This includes particularly the weight of the
diaphragm which in radio receivers is generally
lighter than the diaphragm used in the ordinary
wire telephone receiver.
A series of experiments conducted by
Dr. Austin indicate that the average tele-
phone produces the greatest volume of
sound when the frequency of the alternat-
ing current passed through the windings
varies from 300 to 500 cycles per second.
Frequencies in excess of 500 cycles de-
crease the amplitude of vibration of the
telephone diaphragm and hence produce
less sound.
In view of the foregoing, a transmitter
having a spark frequency of 600 to 1,000
sparks per second gives better response in
the head telephones than one of lower
frequency. Part of this is due to the fact
that the human ear is more responsive to
the higher frequencies than to those of
lower pitch.
Telephones of 75 to 150 ohms resist-
ance, if used with the magnetic detector,
the tikker, and the three element vacuum
valve gives good response, but other re-
ceiving detectors, such as the crystal recti-
fiers, require telephones of at least 2,000)
ohms resistance. Telephones of 15,000)
ohms resistance have been constructed but:
such a winding is not required for the
average radio receiver.
A telephone receiver possessing a notable
degree of sensitiveness has been recently developed in the United States by T. Baldwin.
The essential parts of this receiver are indicated in the diagram, Fig. 195a, where a ring:
shaped horseshoe magnet with . poles N and S is fitted with two "U" shaped soft iron
pieces, P-l and P-2. The telephone winding W, placed longitudinally between these pole
pieces, has a slot in the center in which is placed a soft iron armature balanced on the
pivot P-3. One end of the soft iron armature is connected by the brass wire R to the mica
-c-
-D-
Fig. 195a, b, c Construction and Circuit
the Baldwin Telephone.
kECElVlNG CIRCUITS, DETECTORS, TUNING APPARATUS.
169
Or isinglass diaphragm M which is screwed under the receiver cap as in the ordinary
telephone. During the passage of a fluctuating current through the winding W the soft
iron armature A is thrown into vibratory motion and the vibrations transferred to M.
A prominent feature of this receiver is the fact that the armature A is under no magnetic
strain until a fluctuating current flows through the ^vinding W.
The fundamental principle of operation is as follows : The diagram, Fig. 195b, shows
the direction of the lines of force of the permanent magnet through the pole pieces, and
as will be observed the flux divides equally between both sides of the "U" shaped poles
and continues through the magnet. Due to this division of flux, there is no strain on the
armature A, a condition just opposite to that found in the ordinary telephone receiver,
where the diaphragm is drawn toward the core of the magnet and held under considerable
tension.
If current flows through the winding in a given direction and the permanent magnet
were removed, the resultant flux would have the direction indicated by the arrows, Fig.
195c, that is, the direction of the flux would be lengthwise of the winding and would cir-
culate in the direction shown. Under such conditions, the armature would be equally
attracted to the lower and upper pole pieces and remain in a neutral position.
If a direct current, let us say, circulates through the winding from an external source,
as in Fig. 195d, then the lines of force issuing from the permanent magnet and from the
electromagnet will oppose in some parts of the magnetic circuit, but in other parts of the
circuit they will flow in the same general direction. In the particular example cited, the
fluxes will oppose on the left hand side of the upper pole piece and in consequence the lines
of force will flow to the right hand pole piece and from that point on circulate through
the core of the perma-
nent magnet, as shown
by the long arrows.
The effect of this
will be to attract the
armature A to the left
hand side of the lower
pole piece and to the
right hand side of the
upper pole piece and the
mica diaphragm will
then be deflected up-
ward. . If current is
passed through the
winding in the opposite
direction, the actions just
Fig. 196— Diagram Showing the Principle of Microphonic Relay. described Will be re-
versed and the dia-
phragm will be deflected in the opposite direction. The entire action is thus seen to be
much similar to a polarized relay.
The sensitivity of this telephone can be accounted for first, by the fact that the magnetic
circuit is one of low reluctance; second, the armature of the magnet ^is under no strain
until current passes through the receiver winding, hence a greater deflection of the dia-
phragm is obtained; third, the armature is acted upon at both ends and since the flux is
produced differentially like that in a polarized relay, the deflection for a given magnetizing
current is accordingly increased.
151. Microphonic Relays or Sound Intensifies. — A microphonic relay has
been developed for intensifying the currents flowing in the local circuit of a wire-
less telegraph receiver, but owing to the difficulty experienced in maintaining the
instrument in a permanent state of adjustment, it has not been commercially
adopted.
A working idea of the relay may be obtained from diagram, Fig. 196, wherein the tele-
phones are removed from the local circuit of a given receiving set and the microphonic
relay winding W substituted. Immediately in front of the magnet is placed a diaphragm
which may be tuned mechanically to the spark frequency of the transmitter.
The diaphragm carries the carbon button A; the second carbon button B is attached
to an adjustable screw, the two buttons being placed in light contact with each
other. A local battery of 1^2 to 6 volts is joined in series with the microphonic contact
170
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 197a — Brown Amplification Relay for Increasing
Radio Signals.
and the circuit continues through the head telephones P-l. During the reception of radio
signals the vibration of the diaphragm P causes greater vibration of the diaphragm of the
head telephone P-2 due to the larger value of current flowing through the local circuit than
through the circuit of B-l.
If a number of these relays are connected in cascade, the signals will be increased from
20 to 30 times their original strength. Extremely careful adjustment of the microphonic
contacts is required for the best response.
152. Brown Amplifying Relay. — A particularly successful microphonic
relay has been developed by S. G.
Brown. This relay has been employed
by the Marconi Company for trans-
oceanic communication in connection
with carborundum crystals with good
results.
The approximate mechanical construc-
tion and the electrical circuit of one type is
shown in Fig. 197a, where the soft iron
cores K, K, are magnetized by a perma-
nent magnet with the poles N and S. A
fine wire winding W-l encircles the upper
end of the core and a larger magnet wind-
ing W-2 the lower end. Directly above the
core of W-l is a steel vibrating tongue R
carrying the contact D, which touches
lightly contact C, the latter being adjust-
able by a screw. The contact mounted on
the screw adjustment is made of a special osmium-iridium alloy and the other contact is
a button of carbon which, when pressed lightly against the upper point constitutes a
microphone. Winding W-2, telephone P, dry cell battery B, are all connected in series
with the microphonic contact. The current to be amplified enters winding W-l at A ami C
and the resulting change of flux in the core of the magnet moves the vibrating tongue R,
which, in turn, varies the current of B,
causing sounds in the head telephone.
The amplitude of the vibration of R is
increased by the current of battery B cir-
culating through the winding W-2. In
other words, the fluctuating microphone
current is repeated back to the magnet
through winding W-2 and the vibrations
of R magnified accordingly.
If three or four of these relays be
connected in cascade considerable ampli-
fication of the incoming signal will be ob-
tained. For the cascade connection, the
telephones are removed from the local cir-
cuit of the first relay and another winding
of the second relay like that of W-l con-
nected in its place, and so on throughout
the series.
A small milliameter M is connected in
series with the telephone and when the
current flow is 8 to 12 milliamperes, the
relay is in the most sensitive adjustment.
A Brown relay of another type is shown in Fig. 197b, where M is a microphone chamber
filled with carbon granules, the pressure on which can be carefully regulated by means of
an adjusting screw. The vibrating tongue R is acted upon by the flux of the poles A, B.
and the corresponding fluctuations of the battery B-2 not only circulate through the wind-
ings W-2 and thereby amplify the vibrations of R, but these currents also pass through a
step-up transformer, having the primary winding P and the secondary winding S. The
current induced in S flows to the condenser C (of about 2 microfarads capacity) and through
the head telephones. The battery B-2 is one of about 6 volts pressure.
Fig. 197b — Supersensitive Brown Amplification Relay.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
171
Like the first type described, several of these relays may be connected in cascade for
progressive amplification of the incoming radio signals.
153. Atmospheric Electricity. — When the aerial wire of a radio station is
suspended above the earth, it not only absorbs a certain amount of energy from
passing electric waves, but it will be set into oscillation by irregular discharges of
so-called atmospheric electricity which
is termed throughout the United States
"static" and in foreign countries ''at-
mospherics" or "strays."
During the spring, summer and autumn
in the northern zones of the United States
the potential of the air seems to be higher
than that of the earth and in consequence
a discharge takes place through the aerial
conductors to earth at irregular intervals.
This induced current causes a crackling,
irregular sound of more or less intensity
in the telephones of the receiving set which
may interfere to a marked extent with the
reception of radio signals.
Widely varying theories exist as to the
probable origin of static discharges, but a
considerable amount of this interference is
quite likely set up by nearby or far distant
electric storms. Just as the transmitter of
a radio station sets up electrical oscilla-
tions of more or less damping, in u the re-
Fig. 197c — Details Brown' Relay.
ceiver aerial, so also the discharge of lightning between two oppositely charged clouds or
between the clouds and the earth sets up a highly damped electric wave which will set
practically any receiving aerial into vibration at whatever frequency it happens to be
adjusted.
Static electricity is especially prevalent in tropical countries and in the northern zones
of the United States during the summer months of the year, but during the night hours
it is apt to be strong in the northern zones during the colder months of the year.
To reduce the interference of static the transmitting apparatus is designed to
produce a spark note of high pitch having a more or less musical tone. The dots
and dashes can then be readily distinguished at the receiving station due to the
difference in the pitches of the interfering static discharges and that of the spark
at the transmitting station. Modern transmitters employing current of 500
cycles produce a musical spark permitting communication to be carried on under
conditions when it would not be possible with a spark note of irregular pitch such
as is obtained with irregularly acting spark gaps.
When the receiving apparatus is connected to very large aerials, severe static
discharges are obtained day or night throughout the year and in order to carry
on communication through this interference, a transmitter of very great power
that will permit the signals to be heard above the static discharges is employed.
Various local appliances have been devised to overcome the interference of static, but
none have been so far highly successful. Balancing circuits have been devised by the
Marconi Company with which they have achieved good results (described in following
paragraph).
With ordinary receiving apparatus, the operator, at any given radio station, may
partially reduce static interference by employing the least possible degree of coupling be-
tween the primary and secondary windings of the receiving tuner, the respective windings
being mechanically drawn apart to a distance consistent with the strength of signals in the
head telephones. Occasionally static interference can be minimized) by throwing the primary
and secondary circuits out of resonance or in case a carborundum rectifier is employed as
the detector, by the application of an abnormal local E. M. F.
With sensitive receiving apparatus, such as the repeating three-element oscilla-
172
PRACTICAL WIRELESS TELEGRAPHY.
tion valve or the step-up valve amplifier, the static signals are enormously
amplified and the good effects of these receivers are aften thus offset.
Hence when atmospheric electricity is especially severe, radio traffic may be more
readily dispatched from station to station by means of a less sensitive receiving
detector, such as the carborundum rectifier or by the Marconi magnetic detector.
An interesting aspect of the static
PI PZ interference is the fact that it does
not persist at certain months of the
year in certain localities, being strong
for a period of several days and then
sometimes disappearing for a space
of a week or more. This may be fol-
lowed by a period of several days,
during which the interference from
this source is exceptionally strong,
but, as stated previously, the high
pitched note of modern transmitters
to a large extent overcomes the
difficulty.
154. The Marconi Balanced Crystal Receiver (English Marconi Company).
—No apparatus or circuit has so far been devised to completely eliminate the in-
terference of static discharges. However, communication can be effected by the
circuits of the Marconi balanced crystal receiver when with ordinary circuits it
would not be possible. In fact, the balanced crystal tuner often reduces the inter-
ference from this source to a marked degree.
The complete circuits of the balanced crystal receiver are shown in the diagram, Fig.
198, where the secondary winding of the receiving tuner is represented by the coil L-l,
Fig. 198 — Circuits of Marconi's Balanced Crystal
Receiver. (English Marconi Company.)
the secondary condenser
at P-l and P-2, the bat-
tery at B and the tele-
phones at P.
To carry out the fun-
damental principle of this
receiver, crystals D-l
and D-2 must have like
volt-ampere characteris-
tics, and, accordingly,
crystals are specially se-
lected for the purpose.
Briefly, the action of
this circuit can be de-
scribed as follows: If
crystals D-l and D-2 are
adjusted to the same
degree of sensitiveness,
their currents will act
equally and oppositely
upon the telephone P,
and no signals will result.
If, however, D-2, let us
say, is adjusted to a high
degree of sensibility and
D-l to a lesser degree,
signals will be received.
Under these condi-
at C-l, the opposed crystals at D-l and D-2, the potentiometers
20-
16-
CHANGE OF CURRENT IN D-2 FOR NORMAL SIGNAL
IN D-l FOR NORMAL SI6NAI
CURRENT OF B OPPOSES CURRENT OF
199 — Curve
VOLT 5
Showing Principle
of Balanced Crystal Receiver.
tions, if an extra severe discharge of static passes through the aerial circuit, almost equal
effects are produced in the head telephone P by both crystals, and the crashing sounds ordi-
narily experienced partially eliminated.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
173
The real effect of the balanced crystal receiver is to limit the sound produced in the head
telephones, advantage being taken of the peculiarities of the volt-ampere characteristic curve.
This can best be explained by the curve, Fig. 199, where the point X represents the adjust-
ment of the potentiome-
ter P-2 for the crystal
D-2, that is, it is the
point where the addition
of a slight antenna E.
M. F. will cause the cur-
rent in the head tele-
phone circuit to increase
to the point Y. On the
other hand, point X1
(lower down on the
curve) is the adjust-
ment corresponding 'to
the crystal D-l, where
it will be seen that the
same value of antenna
voltage which will cause
a large increase of cur-
rent in detector D-2 will
cause but a small in-
Fig. 200a— Type I Aerial Changeover Switch.
CONNECTOR TO OSCILLATION
TRANSFORMER AND AERIAL
crease of the current through the local circuit of detector D-l. The current corresponding to
D-l, is shown at Y1 on the curve (which is really a negative current).
Hence the current of crystal D-2 predominates, and although signals will be received
from any given station, they will not equal in strength the signal to be obtained by the use
of one crystal.
If an extra severe discharge of static strikes the receiving aerial, due to its extraordinary
intensity, the current in the local circuit of detector D-l reaches approximately the same maxi-
mum as in D-2, or, in
other words, the current
increases to approxi-
mately point Y on the
curve, but the current of
D-l opposes that of D-2,
and hence both detectors
act almost equally and
oppositely on the receiv-
ing telephone, and the
crash of the static dis-
charge will be largely
annulled. The intensity
of strong radio signals
will be reduced in the
same manner.
The adjustment for ob-
taining the best operat-
ing characteristic of this
combination is readily
obtained by a skilled op-
erator. First, the sensi-
tive spots on crystals D-l
and D-2 are located, fol-
big. 200b — Type I Aerial Changeover Switch. , , , ,.
lowed by corresponding
variation of the sliding contacts of the potentiometers P-l and P-2.
155. Type I Aerial Changeover Switch. — A plan view and side elevation of
this switch appear in Figs. 200-a and 200-b, respectively. Several steel discs, B,
which make connection with the spring contacts C on either side of the rod, are
mounted on a hard rubber rod R. When the handle A is thrown downward a long
CIRCUIT TO TRANSFORMER
/ PRIMARY CLOSED HERE
I
\
\
\
174
PRACTICAL WIRELESS TELEGRAPHY.
ANTENHA SWITCH
TYPE H* 1
steel bar F closes the circuit to the primary winding of the power transformer
through the contacts 11 and 12. In the opposite position the bar separates the
spring contacts M, M1 200-a, which disconnects the transmitting oscillation trans-
former from the aerial during the pe-
riod of reception, preventing the in-
coming oscillations leaking to earth.
The various circuits closed by the
discs mounted on the hard rubber rod
place the detector and head telephone
on short circuit during the period of
• • + n T/f jMjJL \ f transmission. They may also be em-
' jjj"|^m»|| ^ ployed to start and stop a motor blozver
I I 14— 3 i I or an automatic motor starter. The
^ ' < f type I switch is supplied with Marconi
transmitting sets up to 5 K. W. ca-
pacity.
For the use of operators in the Marconi
service, the circuit diagrams, Figs. 201, 202
and 203, are published, showing the con-
nections in Fig. 201 of the type I antenna
switch to the external binding posts of the
type 106 receiving tuner, and in Fig. 202
the connections of the type S, H, aerial
changeover switch to the external binding
posts of the type 106 tuner. The diagram,
Fig. 203, shows the connections of the type
I antenna switch to the external binding
posts of the type 107-a receiving tuner.
In the diagram, Fig. 201, binding posts
2, 4 and 5 of the type I antenna switch
short circuit the crystal detector and the
Tune?!** head telephones during transmission. Bind-
ing post No. 1 connects to aerial binding
post No. 1 of the type 106 tuner. Contacts 11 and 12 close the circuit to the primary winding
of the transformer. The binding posts 6, 7, 8 and 9 of the type 106 tuner are connected to
the four binding posts of the battery box as shown.
In the diagram, Fig. 202, posts 1, 2, 4 and 5 of the type S. H. antenna switch lead to
contacts which place the head telephone and detector of the type 106 tuner on short circuit.
Binding posts 11 and 12 close the circuit to the primary winding of the transformer.
In the diagram, Fig. 203, posts 2, 4 and 5 of the type I switch lead to contacts which short
circuit the receiving detector and the receiving telephones. These diagrams should be care-
fully studied and in event that the wiring is
taken down, the connections shown should
be carefully duplicated.
156. Type 112 Receiving Tuner.
— This receiving tuner was pri-
marily designed for use with the
special l/% K. W, cargo type transmit-
ter developed by the Marconi Com-
pany and fundamentally is similar* to
'the" type 101 and" type '106 tuner, but
the construction is considerably simpli-
fied. A front view is shown in Fig.
203-a and a side view in Fig. 203-b.
As will be seen in the wiring diagram,
Fig. 203-c, the circuits are similar to those
shown in Fig. 153-b, the potentiometer,
battery and head phones .being shunted
ANTENNA
SWITCH
TYPE'SH"
TO KEY
TO CHARGING PANEL
Fig. 202 — Type S H Switcn Connected to Type 106
. . ' Receiving Tuner.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
175
around the fixed condenser. A buzzer test circuit is placed in inductive relation to the
earth lead and the buzzer is thrown into operation by means of a small push button mounted
on the front of the panel.
The receiving transformer is of the inductively coupled type consisting of a two-layer
primary and a two-layer secondary winding, the inductance of the primary winding being
regulated by a "tens" switch and a "units" switch. The "unit" switch cuts in ten single
turns in the primary winding and the "tens" switch ten turns at a time
The inductance of the secondary winding is altered by a simple multi-point switch.
The secondary shunt condenser consists of two concentric brass tubes, which are telescoped
by a small knob in the slot on the top of the panel.
l"l, TUNE Q
2 CELLS
DRY BATTERY
TO CHARGING PANEL ^" •
Fig. 203 — Type I Switch Connected to Type 107a Receiving Tuner.
The coupling between the primary and secondary windings is altered by a knob sliding
in the lower slot to the front of the panel. When the knob is placed to the extreme left
the coupling is maximum, lesser degrees being obtained by moving this knob in the opposite
direction.
The series antenna condenser is thrown in the aerial circuit by means of the switch
marked "condenser-in-out." This condenser is of fixed value, the necessary adjustment
for resonance being obtained at the primary inductance.
The type 112 tuner is fitted with a carborundum detector, the latter being mounted
immediately to the front of the panel. The local battery current for the crystal is turned
on and off at the switch marked "battery-on-off." This switch should always be in the
"off" position when the receiver is not in use.
176
PRACTICAL WIRELESS TELEGRAPHY.
A sensitive spot is found on the crystal by pressing the push button and "feeling about"
on the crystal with the pointed contact until the loudest response is obtained, simultaneous
adjustment being made of the potentiometer.
The receiving transformer is adjusted to the incoming signal as follows:
(1) Adjust detector by buzzer tester.
(2) Place the coupling knob as far to the left as possible.
(3) Vary inductance of the primary and secondary windings progressively
until the desired station is heard.
(4) When signals are heard decrease the coupling slightly.
(5) Then retune primary and secondary circuits, using slight values of capacity
at the secondary condenser.
(6) Then slightly vary the coupling until loud signals are obtained or until
an interfering signal is eliminated.
KTICTOR
5UZ7EK TESTER
fcf— il
•o* *
POTENTIOMETER
Fig. 203a — Front View of the Marconi Type 112 Receiving Tuner (The American Marconi Company).
156a. General Advice for the Manipulation of a Receiving Tuner. —
While learning to manipulate a receiving tuner of any type, the student should
first study a complete fundamental wiring diagram of the set and note the corre-
sponding parts on the actual equipment. He should observe particularly the
direction in which the inductance, changing switches and the variable condenser
control knobs are moved for an increase of their values. It should always be
borne in mind that any increase or decrease of wave length adjustment
in the antenna circuit should be followed by a similar increase or decrease in
the secondary circuit. Also a change of coupling slightly influences
the effective self-inductance of the primary and secondary windings, and therefore
if the inductance of either winding is adjusted for a given wave length, and after-
ward the coupling decreased to minimize interference, a new value of inductance
must be selected at the primary and secondary coils ; or, if the period of these
circuits is varied by means of variable condensers, a slight change in capacitance
should be made.
RECEIVING CIRCUITS, DETECTORS, TUNING APPARATUS.
177
(a) It should be remembered in adjusting a station for the first time that the adjust-
ments of any given tuner will vary with the different aerials. If the tuner is also
strange to the operator, the best method to pursue is to tune first the standard 600
meter wave, using a rather large amount of inductance and relying upon the series
condenser to vary the antenna) wave length to pick up signals, thereafter reducing the
inductance and eliminating the short wave condenser until the maximum strength of
signals is obtained.
(b) If a call is expected from one of several wireless stations not accurately tuned
to the same wave length, close coupling should be employed between the primary and
secondary windings and the shunt secondary condenser set at zero, but after communi-
cation is established, lesser values of coupling should be employed to prevent
interference. (See Section H appendix.)
Fig. 203b— Rear View of Marconi Type 112 Receiving Tuner (The American Marconi Company).
(c) Due to the fact that the wave length of the average ship's aerial lies between
300 and 600 meters, only a few turns of inductance are required to adjust the antenna
system to the wave length of 600 meters. On the other hand, the short wave variable
condenser must invariably be employed to obtain the 300 meter wave with a ship's
aerial.
(d) If the tuner is fitted with a primary shunt condenser, increased selectivity may
be obtained by proper selection of capacity values, but generally with decreased
strength of signals.
(e) Severe discharges of atmospheric electricity may temporarily or permanently
destroy the sensitiveness of a receiving detector, hence frequent readjustment is neces-
sary during an operating schedule. These remarks, however, do not apply to a highly
exhausted three-element vacuum valve, the magnetic detector, the Fleming oscillation
valve, or others which possess a marked degree of stability.
(f) Frequent use of the test buzzer will indicate whether or not the crystal detector
is in adjustment. It has been observed that the adjustment of the crystal detector
giving good response to a buzzer is not necessarily the most sensitive adjustment for
a far distant station, and similarly with most types of receiving detectors, the adjust-
178
PRACTICAL WIRELESS TELEGRAPHY.
ment giving maximum response to nearby stations, is not the most sensitive adjust-
ment for a far distant transmitting station.
(g) Not all carborundum crystals possess equal degrees of sensitiveness; conse-
quently those giving maximum response to far distant stations should be used.
(h) The maximum degree of selectivity is obtained in receiving circuits of radio-
frequency when the loosest coupling which will give a readable signal is employed
and when inductance is used to tune aerial circuits and some capacity is used in
shunt to the secondary coil.
WIRES 1,1,4,5 CONNECT TO TYPE I AERIM. SWITCH
Fig. 203c— Complete Wiring Diagram of the Type 112 Receiving Tuner (The American Mar-
coni Company).
(i) The diaphragm of receiving telephones should frequently be removed and
carefully wiped to prevent the formation of rust. Bent diaphragms should be imme-
diately replaced by new ones. The diaphragm should not touch the surface of the
magnet.
(j) If in doubt concerning the continuity of the circuits of a receiving tuner, a
testing circuit comprising a dry cell battery and a head telephone connected in series
should be applied to the primary and secondary coils to ascertain if the circuit is in
conductive condition.
PART X.
AUXILIARY APPARATUS OR EMERGENCY
TRANSMITTERS.
157. STATUTE REQUIREMENTS. 158. TUNED COIL SET. 159.
THE ELECTRIC STORAGE BATTERY COMPANY'S ACCUMULATORS
AND CHARGING PANEL.
157. Statute Requirements.— The United States Statute (Act of August 13,
1912), requires that all vessels carrying radio equipment be fitted with an emer-
gency transmitter which can be operated independently of the ship's generator.
This sender must have a daylight transmission range of at least 100 miles, and
must be capable of functioning continuously for a period of four hours. If an
independent emergency transmitter is not supplied, a source of auxiliary power
of sufficient capacity to operate the motor generator independently of the ship's
generator must be available. The regulations of the International Radio Tele-
graphic Convention require the emergency apparatus to be capable of functioning
for at least six hours, and to have a minimum range of 80 nautical miles in case of
a ship having constant radio service, and 50 miles where the ship's station has a
service of limited duration.
Certain vessels of the American Marconi Service are fitted with a 60 cell stor-
age battery of capacity varying from 60 to 224 ampere hours. The batteries of
lower capacity simply furnish current for the operation of the motor generator, but
those of higher capacity are employed to operate a few emergency lights as well.
The 60 cell battery generally the property of the Steamship Company is under the
direct supervision of the Chief Engineer, but the operators of the Marconi Com-
pany must have sufficient knowledge of the circuits and the manipulation of the
charging panel to keep the batteries in a fully charged condition.
If for any reason, a 60 cell battery is not supplied, an emergency transmitter
developed by the Marconi Company is employed. This sender consists of a 10-
inch induction coil operated by a 30-volt storage battery, the induction coil being
employed to excite the condenser of the power set in place of the usual high voltage
transformer.
The auxiliary transmitter, originally planned by the Marconi Company, is
shown in Fig. 204, where the spark gap of a 10-inch induction coil is connected
directly in series with the aerial system, the primary winding being energized by
a storage battery of 24 to 30 volts. Provision was made on some ships whereby
these coils could be operated either directly from 110 volts D. C., with a special
rheostat connected in series or from the storage battery.
The apparatus shown in the circuit of Fig. 204 has been termed the (tplain
aerial set" because the spark gap is connected directly in series with the antenna
circuit. The use of the plain aerial transmitter is not allowed by the United States
regulations except in case of emergency, because when no extra inductance is
inserted at the base of the antenna system, a highly damped wave is radiated
which will interfere with the dispatch of traffic between other stations.
180
PRACTICAL WIRELESS TELEGRAPHY.
158. Tuned Coil Set. — When the induction coil is employed to excite the
closed circuit condenser as in Fig. 205, it is called the "tuned coil set." The great
advantage of this connection lies in the fact that the antenna oscillations will be
damped out less rapidly than with the "plain aerial" connection, and the radiated
wave will cause less interference to the operation of other stations.
A description of the circuits follows : The apparatus of the power set is represented by the
alternator armature A, C, the primary winding of the closed core transformer P, the circuit
including the wattmeter W. The secondary circuit comprises the secondary winding of the
transformer S, the high potential condenser C-l, spark gap G and the primary winding of the
oscillation transformer P-l. The aerial circuit is represented by the secondary winding S-l,
the short wave condenser C-2 and the aerial tuning inductance S-2.
The circuit of the emergency induction coil extends from the D. C. switch at the left of
the drawing, though the underload circuit breaker B, through the regulating resistance R, to
a 24-30-volt storage battery shunted by a small voltmeter V. The charging resistance R is
proportioned to pass from 6 to 7 amperes through the storage battery during the charging
process. The function of the underload circuit breaker has been described in Part V, and
it is sufficient to say here that it automatically opens the circuit in case the voltage of the
generator falls below that of the storage battery.
Z4VOLT STORAGE
BATTERY
6V.
6V.
Fig. 204 — "Plain Aerial" Emergency Transmitter.
(a) Adjustment and Timing of the Set. To place the storage battery on
charge, the D. C. switch is closed and the plunger U of the underload circuit
breaker pushed upward by hand, the charging circuit thereby being closed through
the contact points E, E.
The circuit from the battery to the induction coil may be traced through the
telegraph key, through the primary winding of the induction coil P-3, and thence
through the interrupter I, the vibrator condenser being represented at K. In
order that a uniform spark discharge may be obtained, careful adjustment must
be made of the stationary contact of the interrupter I until a discharge free from
arcing is secured, but generally at its best the pitch of the note produced by these
coils will be rather low.
In case of accident to the power apparatus, such as the burning out of the motor generator
or the high potential transformer, the emergency transmitter is put into action in the follow-
ing manner: The switch H-2 is placed in the downward position. This connects the tele-
graph key in series with the primary winding of the induction coil. Next the plug contact
AUXILIARY APPARATUS OR EMERGENCY TRANSMITTERS.
181
R-4 is removed from the connector R-l and plugged into R-3, thereby connecting the secon-
dary winding of the induction coil to the condenser C-l. (A single blade double-throw high
voltage switch is often used instead of the flexible plug connector.) After these connections
have been made, the telegraph key is pressed and the vibrator of the induction coil adjusted
simultaneously until uniform interruptions are secured. Generally with this connection, it
becomes necessary to reduce the length of the spark gap G, and in case a quenched spark gap
is employed, to use no more than two or three plates. If a rotary gap is included in the power
transmitter, it must be stopped with the spark electrodes in such position as will afford a dis-
charge gap of the correct length for the coil. Since the closed and open oscillation circuits
of the transmitter are already adjusted to resonance, the complete process of tuning need
not be gone over again, with the exception that the coupling between the primary winding
P-l and the secondary winding S-l may have to be increased.
The ammeter connected in the antenna circuit of this set should read from 2 to 3 amperes,
depending upon the electrical dimensions of the circuits of radio-frequency, or, in other words
the type of set. The range of transmission varies from 125 to 225 miles in daylight.
AUXILIARY TRANSMITTER
CIRCUIT
Fig. 205 — Tuned Coil Emergency Transmitter.
The coil transmitters are generally supplied with the portable chloride type
D-5 accumulator of the Electric Storage Battery Company, but later installations
are equipped with another type known as the 5 K. X. portable accumulator, either
battery being of 60 ampere hours capacity.
The general instructions given for the chloride battery in Part V, apply to the
batteries of these sets, and should be carefully observed. It will be noted from
the diagram of Fig. 205 that the battery can be placed on charge with the induc-
tion coil in operation. As a safety measure, to prevent the meter being burned
out by electrostatic induction from the transmitter, the voltmeter circuit contains
a small strap key, which must be closed to take a reading of the voltage of the cells.
159. The Electric Storage Battery Company's Accumulators and Charging
Panel. — The type and rating of the Exide cells furnished by the Electric
182 PRACTICAL WIRELESS TELEGRAPHY.
Storage Battery Company for auxiliary power is shown in the following
table :—
TYPE RATING
60 cell 7 PV — 72 ampere hours;
60 cell 11 NV— 140
60 cell 13 MV— 168
60 cell 17 MV— 224
Type 7 PV battery is employed in connection with the ^2 -kilowatt panel trans-
mitting set, type P-5 of the Marconi Company. The other types are for opera-
tion of the 2-kilowatt, 500-cycle motor generators furnished with Marconi type
P-4 set and also for auxiliary light aboard the vessel.
A photograph of the E. S. B. Co.'s charging panel is shown in Fig. 206, and
a fundamental diagram of the connections from the board to the batteries and
motor generator in Fig. 207. The latter diagram includes the complete connec-
tions of the Marconi 2-K. W. 500-cycle Crocker-Wheeler type of motor generator,
and the automatic starter. Fig. 208 shows a rear view of the wiring of the panel.
Fig. 205a— Charging Panel Used with Marconi Tuned Coil Sets.
In the diagram of connections, Fig. 207, the connections for the voltmeter and
the double-pole double-throw switch and other switches for auxiliary lighting
service are purposely left out to simplify the drawing, but a detail of the volt-
meter connection appears in Fig. 208.
Returning to the diagram of Fig. 207: All apparatus concerned in the charge and dis-
charge of the batteries appear to the left of the drawing, and the circuits of the automatic
starter to the right, including the wiring of the motor generator. A six-pole double-throw
switch, with knife-blades 1, :2, 3, 4, 5, 6, when thrown up in the drawing or to the left on the
actual charging panel, places battery units A and B on charge, but in the opposite position, on
discharge], the circuits from the battery continuing through the blades 5 and 6 to the auto-
matic starter and motor generator.
The resistance coils R-l, R-2 and R-3 are connected in the charging circuit of battery A,
through the knife blades 1 and 2 and coils R-4, R-5 and R-6, through the blades 3 and 4 to
battery B. The overload circuit breaker K is connected in series with the common charging
lead of battery units A and B. The winding of the no-voltage release magnet for this breaker
indicated at N has the series protective resistance R-l. Contacts C-l and C-2 mounted on
AUXILIARY APPARATUS OR EMERGENCY TRANSMITTERS. 183
LEAK LAMP
VOLTMETER
SWITCH
AMPERE HOUR
METER
POLARITY REVERSING
- SWITCH
CHARGING
POSITION
L1GHT5 FROM
GENERATOR
UNDERLOAD AND
ERLOAD BREAKER
_VOLTMETER
_J>I5CHARGE SIDE
OF SWITCH
LIGHTS FROM
"""BATTERY
Fig. 206 — Standard Charging Panel Supplied by the Electric Storage Battery Company for Marine Use.
184
PRACTICAL WIRELESS TELEGRAPHY
wwwvw-
c£
-HWWWVW-h
AUXILIARY APPARATUS OR EMERGENCY TRANSMITTERS.
185
the circuit breaker open the circuit of the no-voltage release magnet when the breaker trips.
It should be thoroughly understood that this breaker will open the charging circuit in case
of an overload during the charging period, or in case the voltage of the generator falls below
the voltage of the battery. The breaker will also open when the pointer on the ampere-hour
meter touches the contact point at the zero position (during the charging process).
CHARGING RESISTANCES
FOR BATTERY "A"
CHARGING RESISTANCES
FOR BATTERY '&"
AUX OPINING SW.
OPENS WHEN.
CB. OPENS
RESISTANCE
LOW VOLTAGE
Fig. 208 — Rear View Actual Wiring Diagram of Electric Storage Battery Company's
Charging Panel.
P-l and P-2 are 25-mzff incandescent lamps which are shunted around the circuit
breaker and the resistance units. Through these, a small value of charging current con-
stantly flows through the cells, compensating for local losses, such as may be caused by
local action or a slight surface leakage of the cell.
186
PRACTICAL WIRELESS TELEGRAPHY.
TO DISCHARGE MAINS
GO CELLS IN SERIES
An important part of this apparatus is the double pole double throw reversing switch
placed in the upper left-hand corner of the drawing. Should the connections from the
ship's generator to the switchboard be reversed, say, during repair or rewiring, the correct
polarity can always be obtained by plugging in the voltmeter connection to the power line,
followed by closing this switch. If the pointer of the meter moves in the proper direction
or across the scale, the polarity of the charging mains is correct. If the pointer moves in
the wrong direction, the double-pole switch must be thrown in the opposite direction. Pro-
tective fuses are inserted in the battery charge and discharge circuits to open the circuit in
case of overload.
The general operating instructions for the Exide cells given in Part V should
have careful attention. The operator should aim to keep the batteries in a fully
charged condition at all times, or confining the remarks to daily practice, the
pointer of the amperehour meter should always be near to the zero position and
if after use of the battery the pointer indicates that a given quantity of current
has been taken out, it should be placed immediately on charge and allowed to
remain so until the pointer returns to the zero position of the scale of the ampere-
hour meter.
One part of this circuit may require explanation. It will be observed that the ampere-
hour meter is merely connected in series with one of the battery units (Battery A) when
on charge. The neces-
sity for this connection
will be evident from the
following explanation :
If the meter were con-
nected in series with
both battery units, the
pointer of the ampere-
hour meter would travel
across the scale at dou-
ble the rate of the actual
charging current flowing
to each battery unit for
the reason that the bat-
teries are connected in
parallel. As an exam-
ple, if the amperehour
meter were connected in
series with both battery
groups on charge and
further that a quantity
equal to ten ampere
hours of current passed
from the generator to
the battery, each set of
cells actually would re-
ceive but five amperehours of the charging current, or, in other words, the meter would
indicate a value actually double the charging current supplied to each group of cells. Hence
the amperehour meter is simply connected in series with one unit on charge, but in series
with both units on discharge, the assumption being made that the two battery units are in
identical states of charge. Any dissimilarity in the two groups of cells can easily be de-
termined by the readings of the voltmeter during load and proper correction made therefor.
In actual commercial practice, no difficulty is found in keeping both battery units in the
same state of charge from month to month.
A detailed diagram of the voltmeter plug switch is shown in Fig. 209. It will be noted
that a small push button key, connected in series with the voltmeter, must be ^ closed in
order to take the reading. A small resistance or multiplier is connected in series as the
drawing indicates.
Plugs 1 and 2 connect to the terminals of the 60-cell battery with all cells connected in
^H
\
ACROSS SHIPS
- GENERATOR
f t
f
^
]
i
7
\
» <
5
! 1
6
BATTERY
UNIT "B"
DETAIL VOLTNAETEr\ CONNECTION
E.S.B.Co. CHARGING PANEL
Fig. 209 — Detail Voltmeter Connection, Electric Storage Battery Com-
pany's Charging Panel.
AUXILIARY APPARATUS OR EMERGENCY TRANSMITTERS. 187
series. Plugs 3 and 4 connect across the terminals of battery unit A. Plugs 5 and 6 con-
nect to the mains from the ship's generator. Plugs 7 and 8 connect to the terminals of
battery unit B.
Although the circuits of the motor generator and automatic starter indicated in Fig. 207
have been gone over in the chapter on motor generators, the notations in Fig. 207 for the
same circuits will now be explained.
S-l is the motor starting switch which may be closed by auxiliary contacts on the aerial
changeover switch or by a small push button switch near to the transmitting key of the
operator. R-3 is the fixed resistance in series with the automatic starter winding W-l,
which is thrown in the circuit when the starter is in the full running position, that is to
say, it is connected in by the upward movement of the plunger. Resistance R-2 is connected
in series with the relay winding W-2 to prevent an excessive flow of current. Relay wind-
ing W-3 is connected in series with the motor armature and in case of an overload, auto-
matically opens the solenoid winding W-l through the contacts C-5 and C-6. R-4 is the
electrodynamic brake resistance thrown in shunt to the armature when the plunger of the
automatic starter drops downward.
F-l is the shunt field of the motor, the regulating rheostat R-5 being connected in series.
F-2 is the generator field winding with the regulating rheostat R-6 connected in series.
This circuit is closed by the automatic starter at point 5, or, in other words, current does
not flow through the generator field winding until the motor has attained normal speed.
Jt is believed that with the information supplied in this and Chapter 5 at
hand, commercial operators will fully understand the circuits of emergency
battery panels and transmitters and will be enabled to handle them successfully
in commercial working.
Vessels fitted with radio apparatus by affiliated Marconi companies may have
storage cells and charging panels which differ in mechanical construction, but
fundamentally they operate along the same general principles. Specific instruc-
tions for each type of cell or panel are, of course, furnished to marine radio
installations by the manufacturer.
Operators of the Marconi Service should observe carefully the following rules:
(1) Keep battery plates covered with pure water at all times.
(2) Keep the batteries fully charged.
(3) Do not place battery on charge when ship's generator is not running.
(4) Watch the polarity of the charging line and throw reverse switch on
charging panels accordingly.
(5) Examine the connections between all battery cells frequently.
PART XL
PRACTICAL RADIO MEASUREMENTS.
MEASUREMENT OF WAVE LENGTH— DECREMENT— CALIBRA-
TION—TRANSMITTING AND RECEIVING APPARATUS.
160. THE IMPORTANCE OF ELECTRICAL RESONANCE. 161. INDI-
CATORS OF RESONANCE. 162. USES OF THE WAVEMETER. 163.
SIMPLE USE OF THE WAVEMETER. 164. GENERAL INSTRUC-
TIONS FOR TUNING A RADIO TRANSMITTER. 165. TUNING BY
THE HOT WIRE AMMETER. 166. TUNING THE 2 K. W. 500
CYCLE PANEL TRANSMITTER. 167. DETERMINATION OF COUP-
LING. 168. PLOTTING OF RESONANCE CURVES. 169. MEASURE-
MENT OF THE LOGARITHMIC DECREMENT OF DAMPING. 170.
CALCULATION OF THE DECREMENT OF THE WAVEMETER (OR
DECREMETER). 171. WAVEMETER AS A SOURCE OF HIGH FRE-
QUENCY OSCILLATIONS. 172. CALIBRATION OF THE SECONDARY
AND PRIMARY CIRCUITS OF A RECEIVING TUNER. 173. CALIBRA-
TION OF THE OPEN AND CLOSED CIRCUITS SIMULTANEOUSLY.
174. MEASUREMENT OF THE NATURAL OSCILLATING PERIOD OF
A COIL. 175. MEASUREMENT OF ELECTROSTATIC CAPACITY.
176. MEASUREMENT OF THE EFFECTIVE INDUCTANCE OF A COIL
AT RADIO FREQUENCIES. 177. CALCULATION OF INDUCTANCE
FROM THE CONSTANTS OF THE COIL. 178. MEASUREMENT OF
THE EFFECTIVE INDUCTANCE AND CAPACITY OF AN AERIAL.
179. CALIBRATION OF A WAVEMETER FROM A STANDARD. 180.
MEASUREMENT OF MUTUAL INDUCTANCE AT RADIO FRE-
QUENCIES. 181. COMPARATIVE MEASUREMENT OF THE STRENGTH
OF INCOMING SIGNALS. 182. "TIGHT" AND "LOOSE" COUPLING.
183. MEASUREMENT OF HIGH VOLTAGES. 184. TUNING AND AD-
JUSTMENT RECORD.
160. The Importance of Electrical Resonance. — It is essential that the
open and closed oscillation circuits of both the radio-transmitter and receiver be
substantially adjusted to the same natural frequency of oscillation. To place cir-
cuits of radio-frequency in resonance or to adjust them to any desired frequency
of oscillation, standard resonating circuits known as wave meters are employed.
In a previous chapter we have explained that a hot wire ammeter may be employed
for determining conditions of electrical resonance in two coupled circuits, but
there is a disadvantage in this method of tuning, for unless the inductance and
capacity of each circuit are known, the resulting frequency of wave length corre-
sponding thereto, cannot be determined ; hence the utility of the wave meter.
A circuit like that shown in Fig. 210a, consisting of a radio-frequency inductance L and a
variable condenser C constitutes an oscillating circuit of variable frequency, the actual value
for any particular setting of the variable condenser being determined by the equation :
5,033,000
vTc~
PRACTICAL RADIO MEASUREMENTS.
189
where L and C are expressed in centimeters and microfarads respectively. Hence at each
division of the condenser scale, we might mark the particular frequency at which the circuit
oscillates when set into excitation. But since a given frequency of oscillation corresponds to
a luaic. of definite length (if the oscillator were radiative), we can calibrate the scale of the
instrument directly in wave lengths rather than in oscillation frequencies.
LAMP
I.*
0- '
Fig. 210a, b, c, d, e, f, g, h, i, j — Methods for Determining Resonance Between Wave-
meter and Circuit Under Measurement.
If either the inductance of the coil or the capacity of the condenser in the circuit, Fig.
210a, is variable, we may fit the variable element with a scale of wave lengths and the instru-
ment will then be called a wavemeter.
Now if the coil L is placed in inductive relation to any part of an active oscillation circuit,
such as the closed or open circuit of a radio transmitter, radio-frequent oscillations will be
induced in the circuits of the wavemeter when it is adjusted to the frequency of the gen-
190
PRACTICAL WIRELESS TELEGRAPHY.
crating circuit. Some indicator of maximum flow of current or maximum voltage must now
be inserted in the circuit (of the wavemeter) in order that the exact point of resonance on
the variable element may be located.
161. Indicators of Resonance. — That the wavemeter is in resonance with
the circuit under measurement, may be determined by one of several instru-
ments.
In Fig. 210b a milliammetcr M, range 0-200 milliamperes, is connected in series with the
wavemeter for determining the adjustment of maximum current flow.
In Fig. 210c, a small hot wire zvattmeter W , range .01-0.1 watts, is connected to the
secondary winding S, of a small step down transformer, the primary P being connected in
series with the wavemeter.
In Fig. 210d, a small glow lamp G (2 or 4 volt battery lamp), is connected in series with
the wavemeter, the resonant adjustment being determined when tke lamp glows brightest
(with the wavemeter in a fixed position).
In Fig. 210e, a thermo-couple A, B, is attached to a heating wire C, D, the latter being
connected in series with the wavemeter. The terminals of the thermo-couple are connected
to a sensitive milli-voltmeter which may be calibrated in milliamperes.
In Fig. 210f, a rectifying detector D is connected in series with a galvanometer G, both
being shunted across the condenser C. The currents of radio-frequency are converted by
the rectifier to direct current and the
resonant adjustment is determined by the
maximum deflection of the galvanometer.
In Fig. 210g, an electrostatic telephone P
is connected in series with the wavemeter,
the telephone being an active part of the
oscillation circuit. The telephone contains
a winding of three or four turns placed
underneath a copper diaphragm. The max-
imum sound is obtained when the wave-
meter is in resonance with a given oscilla-
tion circuit, the copper diaphragm moving
with the group frequency of the transmitter.
In Fig. 210h, a tube N, filled with neon
gas, has sealed-in terminals at either end.
When shunted across the terminals of the
wavemeter condenser, the tube glows bril-
liantly at resonance.
In Fig. 210i, a crystal rectifier D is connected in series with a 2,000 ohm telephone P, the
final two terminals being shunted across the condenser C. The maximum of sound is obtained
in the telephone at resonance. The connection of 210j is often preferred because the calibra-
tion of the wavemeter is not affected by the presence of a shunt detecting circuit as in 210i.
The uni-polar connection of the detector has the disadvantage that the wavemeter must be
placed in closer inductive relation to the circuit under test than with the connection of 21 Oi.
The inspectors of the American Marconi Company prefer either the hot wire
wattmeter, or the crystal detector and head phones as indicators of resonance
above all others.
162. Uses of the Wavemeter. — The wavemeter may be employed:
(1) To place two or more circuits of radio-frequency in resonance;
(2) To measure the wave length of the closed or open oscillation circuits of
a radio transmitter.
(3) To determine the percentage of coupling between the closed and open cir-
cuits of a transmitter;
(4) To determine the decrement of damping;
(5) To calibrate a receiving set (by means of an exciting buzzer) ;
(6) To determine the wave length of a distant transmitting station at the
receiving station.
(7) To determine the purity of the wave emitted from the antenna.
163. Simple Use of the Wavemeter. — A simple use of the wavemeter is
shown in the diagram, Fig. 211, wherein the natural wave length of an aerial is
to be measured. In the diagram, Fig. 211, S is the secondary winding of an induc-
Fig. 211 — Diagram for Measuring the Natural Wave
Length of an Aerial.
PRACTICAL RADIO MEASUREMENTS.
191
tion coil fitted with a vibrator, S-l a spark discharge gap of simple design con-
nected in series with the aerial A-l. L is the inductance coil of the wavemeter; C
the variable condenser; D a crystal rectifier, and P the head telephone.
When the induction coil is set in opera-
tion a spark discharge takes place at S-l,
the aerial circuit being traversed by groups
of oscillations at a frequency determined by
the distributed values of inductance and
capacity of the aerial, or,
1
Fig. 212 — Showing How an Aerial May Be Set Into
Excitation by Buzzer.
and a corresponding wave motion is prop-
agated through space.
Now if the coil of the wavemeter L
bears the correct inductive relation to the
aerial wire, preferably placed near to the
earth lead, oscillations of maximum ampli-
tude will be induced in the wavemeter cir-
cuits when the wavemeter and the aerial
circuit are in exact resonance. With the
spark discharging at S-l the capacity of the
wavemeter condenser is varied until a clear distinct sound is heard in the head telephones at
a definite setting (of the condenser). The wave length tabulated on the scale underneath
the pointer is that of the circuit under test.
Generally the resonant adjustment of the wavemeter is sharply defined, so that a slight
change in capacity will cause the signals to
disappear. During this measurement, the
operator should take care to distinguish
between the currents induced in the wave-
meter by the oscillations flowing in the
antenna circuit and those set up by electro-
static induction from the induction coil.
The sounds in the telephone due to the
radio-frequent oscillations are heard at a
distinct setting of the wavemeter con-
denser, but the sounds caused by simple
transformer induction can usually be heard
over the entire condenser scale. More ac-
curate readings can be obtained by placing
the coil of the wavemeter close to the earth
lead of the transmitter although when
measuring the fundamental wave length of
the usual ships aerial, by use of a sensitive
crystal rectifier, the wavemeter can be
placed 200 or 300 feet from the aerial, pro-
vided the inductance coil bears the correct
inductive relation to the antenna.
164. General Instructions for
Tuning a Radio-Transmitter. — In
order to tune a Badio-transmitter to the
international standard wave lengths,
the following measurements must be
taken :
I
Fig. 213 — Another Method for exciting Oscillations
in an Antenna by Buzzer.
(1) The natural or fundamental wave length of the aerial;
(2) The wave length of the closed oscillation circuit;
(3) The wave length of the radiated wave.
After the open and closed circuits have been coupled, we must determine :
192
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 214 — Buzzer Excitation Circuit Inductively
Coupled to an Aerial.
(1) Purity and sharpness of the radiaied wave;
(2) The decrement of damping.
(a) Measurement of the Open Circuit. One method of setting the aerial into
excitation and measuring the natural or fundamental wave length was shown in
Fig. 211, but there are several alternative methods by which the antenna may be
set into oscillation.
In the method shown in the diagram, Fig. 212, a condenser C of one microfarad capacity
is connected in series with the aerial and
also across the vibrator of a buzzer B-l
energized by the battery B-2. The counter
E. M. F. of the buzzer windings places an
electrostatic charge on the aerial which dis-
charges at practically its natural frequency.
The capacity of C being very large compared
to that of the aerial, the wave length of the
system is not appreciably altered.
With the buzzer adjusted for clear tones,
the wavemeter, fitted with a crystal rectifier,
is placed in inductive relation to the earth
lead and the capacity of the wavemeter con-
T(C©) ((©) denser varied until a maximum of sound is
X ' \Z±y obtained in the telephone.
In the diagram, Fig. 213, a few turns of
wire are inserted at L-l through which the
circuit of the battery and buzzer is com-
pleted. When the current flowing from B-2
is interrupted by the buzzer, a change in the
strength of the magnetic field takes place about L-l, placing a charge on the aerial system
which discharges at its natural frequency.
A somewhat similar arrangement is shown in Fig. 214, wherein the buzzer circuit is in-
ductively coupled to the aerial circuit through the transformer P, S, the winding S, consisting
of a few turns of wire. The wavemeter is placed in inductive relation to some part of the
open circuit and the wave
CLOSED CIRCUIT length noted by adjusting
the wavemeter to reson-
ance.
The aerial frequently
is set into excitation by
connecting the antenna
and earth wire of an
aerial system across the
vibrator of a buzzer, but
this method of excitation
is not as satisfactory as
the connections of the
two methods shown pre-
viously.
To tune the aerial in
either of the foregoing
diagrams to the standard
wave of 600 meters, turns
of inductance are added
at winding L-2 until the
wavemeter indicates the
Fig. 215 — Showing How the Wave Length of a Closed Oscillation Circuit
is Determined.
wave length to be 600
meters. Generally from
10 to 20 microhenries of inductance are included at L-l to constitute the secondary winding
of the oscillation transformer, the additional turns required for any standard wave being
added in the aerial tuning inductance.
The aerial is tuned to the 300 meter wave by connecting the short wave condenser in
series with the aerial system. A reading is then taken on. the wavemeter, to note the reduc/-
PRACTICAL RADIO MEASUREMENTS.
193
V
m
tion of wave length. If the length of the wave exceeds 300 meters, turns are taken out at
L-2 until the standard wave is obtained. Certain aerials encountered in practical radio have
excessive length for radiating the 300 meter wave even with the aerial tuning inductance cut
out. In a case of this kind, the aerial must be reduced in length or the lead-ins attached to
the center of the flat top rather than to one end.
The correct number of turns for the 450 meter wave are found in the same
manner as for the 300 and 600 meter waves. Generally the short wave condenser
is cut out of the circuit at this adjustment.
(b) Measurement 0/ the Closed Circuit. The closed circuit is tuned to the
standard waves by placing the wavemeter in inductive relation to the primary
winding of the os-
cillation transform-
er, care being taken
to disconnect the
open circuit from
the secondary
winding. The spark
is then discharged — .
in the regular man- lilihl f
ner and the wave ' V' /
length for a given
value of primary
inductance found
on the wavemeter
by means of any of
the resonance indi-
cators described in
paragraph 161.
A diagram of con-
nections for this
measurement is shown
in Fig. 215. Contact
"T" is connected in at
various points on the
coil until the re-
quired wave is found.
With transmitting
sets of large-r rating
the capacity of the
closed circuit con-
denser may have to
be reduced to obtain
the 300 meter wave.
(c) Measure-
ment of the Radi-
ated Wave. The
WATTMETER
Fig. 216 — Showing Method of Determining Length of the Radiated Wave.
next step in tuning is to ascertain if the emitted wave is pure and sharp in ac-
cordance with the U. S. statute requirements. To determine this, the closed and
open oscillation circuits are tuned, inductively coupled and set at the coupling,
giving the highest ammeter reading. (Fig. 216.)
Next a test is made to determine if the aerial radiates all its energy at one wave length.
If the antenna oscillates at two frequencies, two resonant adjustments will be obtained on
the wavemeter and the relative amplitude of the two frequencies can be measured by a zvatt-
meier "W" connected in the circuit of the wavemeter. With the wavemeter in a fixed posi-
tion relative to the antenna, the meter is adjusted to resonance and the relative power at the
two frequencies of oscillation observed. Unless this measurement is taken with caution, the
wattmeter may burn out if the wavemeter is placed too close to the circuits of radio-
frequency.
194 PRACTICAL WIRELESS TELEGRAPHY.
According to the U. S. regulations, the radiated wave is considered as being pure, ivhen
(if the antenna oscillates at tzvo frequencies} the amplitude of the energy corresponding to
the smaller wave is 10 per cent, or less than that in the greater wave.
To determine the relative power of the radiated waves, the capacity of the wavemeter
condenser must be carefully varied, the two maximum readings of the wattmeter correspond-
ing to the two oscillation frequencies being particularly noted. If the wattmeter indicates
0.1 watt at the longer wave, and 0.01 watt or less at the shorter wave, the wave is pure ac-
cording to the United States regulations. If the amplitude of the shorter wave exceeds 0.01
watt, the coupling between the primary and secondary windings must be reduced until the
correct current amplitudes are obtained or until a single wave emission results. It is usual
to reduce the coupling until the antenna radiates a single wave.
That two waves are being radiated from an aerial can be determined by a crystal rectifier
and telephone as well as by the wattmeter, but the relative power of the waves cannot be
determined in this way. If a sensitive vacuum valve detector is connected to the wavemeter,
the latter can be placed several hundred feet from the aerial. The wave length can be
measured with a greater degree of accuracy, due to the "looseness" of coupling.
When a ship's aerial is tuned to the standard waves, near to a building with a
steel or iron frame, the effective resistance and the natural wave length are ap-
preciably altered; hence, to secure the maximum flow of antenna current, the
aerial tuning inductance must be slightly readjusted (when the ship is at sea)
until the ammeter indicates a maximum. Similar effects are observed when a ship
lies near to another vessel equipped with an aerial, particularly if the aerial of the
other vessel is connected to earth. It is preferable to tune a transmitting set at
a distance of at least a half wave length from large metallic structures.
We have defined a pure wave according to the U. S. regulations as being one
in which, if the antenna oscillates at two frequencies, the energy of the lesser
wave will not exceed by 10 per cent, the energy in the greater wave. According
to* the same regulations, a sharp wave is one in which the decrement of damping
per complete oscillation is 0.2 or less. The measurement for the decrement will
be described in paragraph 169.
165. Tuning by the Hot Wire Ammeter. — The open and closed circuits
of a transmitting set can be tuned to resonance as follows : Set the closed oscillation circuit
to a de-Unite wave, or to one of the three standard waves, by means of a wavemeter. Place
the secondary winding of the oscillation transformer in inductive relation to the primary
winding. Follow it by cutting in and out turns at the aerial tuning inductance until the
aerial ammeter indicates a maximum of current.
Next change the coupling and leave the primary and secondary coils at that position,
where a fair value of antenna current is obtained, with the wave emission complying with
the law in respect to sharpness and purity. (The latter is determined by the decremeter.)
The method can be reversed as follows : Set the open circuit to a standard wave by the
wavemeter and place the primary winding of the transmitting oscillation transformer in
inductive relation to the antenna coil. With the spark discharging at normal power con-
sumption, add or subtract primary turns until the highest possible reading of the aerial
ammeter is obtained.
A small glow lamp, such as a 2, 4 or 6 volt battery lamp, shunted by a semi-loop of wire,
serves as an indicator of resonance between the open and closed circuits and is often used
in case of emergency.
166. Tuning the 2 K. W. 500 Cycle Panel Transmitter.— Detailed in-
structions for the tuning of the standard panel sets of the Marconi Company will
be given in Part XII. The process is quite similar to the tuning of any set, with
the exception that the closed oscillation circuit is tuned to the three standard
waves at the Marconi factory and outside of the determination of the logarithmic
decrement all tuning aboard ship can be done by the aerial ammeter alone.
The particular feature of this set is the wave length changing switch, which in a simple
operation permits either the 300, 450 'or 600 meter waves to be radiated, the necessary changes
of self -inductance, condenser capacity, and coupling being selected by a set of blades making
contact with studs leading to various parts of the circuit. The method of tuning this set
will be clear if the following facts are kept in mind :
PRACTICAL RADIO MEASUREMENTS. 195
(1) For any particular wave length adjustment of the transmitter, a critical
degree of coupling between the primary and secondary windings gives
the maximum aerial current.
*(2) The coupling for the quenched spark discharger can be closer than for the
rotary discharger, if the quenched gap is in perfect condition.
(3) The coupling between the primary and secondary circuits of an oscillation
transformer can be varied by increase or decrease of the self-induction of
either coil as well as by drawing the coils apart.
When the quenched discharger is in use, the primary winding bears a fixed mechanical posi-
tion to the secondary winding, but the oscillation transformer is constructed so that they
can be drawn apart for use of the rotary gap. For the quenched gap, the requisite coupling
for each standard wave is secured, by variation of the secondary inductance, turns being
added at the aerial tuning inductance to maintain resonance.
The process of tuning these sets not only consists of adjusting the open and closed cir-
cuits to resonance, but also in locating the proper secondary inductance for the maximum
aerial current. It is more or less a cut and try method, but the skill obtained through
practice enables an inspector to complete the tuning in half an hour. The exact location of
the secondary contact clips can be found more rapidly by turning the coupling handle on the
front of the panel set, and thereby mechanically placing the primary winding closer to the
secondary or farther away. If the primary, for instance, is drawn away from the secondary
and the aerial ammeter registers an increase of current, it is an indication that the coupling
for the final -fixed position of the windings is too close. Hence the primary winding is
brought back to its original position and turns taken out at the secondary, followed by
adding turns at either of the aerial tuning inductances until resonance and maximum read-
ing of the ammeter is secured.
The set should be tuned for the three standard waves, with approximately three turns
cut in at the continuously variable aerial tuning inductance. After the position of the taps
for the secondary winding and the plug aerial tuning inductance are once located, no further
adjustment is required, unless some change in the antenna is made. With these sets the
complete tuning process can be carried out by observation of the aerial ammeter alone, but
the wavemeter should be employed to measure the decrement and to note if two waves are
being radiated.
The tuning of the ^ k. w. set is similar to that of the 2 k. w. set.
In the tuning of a quenched spark transmitter, two or even three points of coupling for
maximum reading of the aerial ammeter are frequently obtained for a given wave length ;
the coupling to be finally selected is that giving the maximum value of aerial current. When
the rotary gaps of these sets are in use, the primary and secondary windings are separated
by a space of 8 to 13 inches, but the coupling position may have to be altered slightly for
each of the three standard waves.
167. Determination of Coupling. — It is customary, in transmitting
systems employing the plain spark discharger, to express the degree of coupling between
the open and closed oscillation circuits in terms of a percentage rather than in terms of the
true co-efficient of coupling. The percentage of coupling is obtained by placing the wave-
meter in inductive relation to the aerial and observing the length of the radiated waves. If
the readings of the longer and shorter waves are squared and their values inserted in the
following formula, the coupling is obtained, or :
X2- — Xis
K = - X 100
\22 -f- Xl2
Where \ = longer wave,
X~ — shorter wave.
The true coefficient of coupling is obtained from the following formula :
M
Where M ^mutual inductance of the oscillation transformer,
L± =self-indUctance primary,
L2 =self-inductance secondary.
*Statements (1), (2) and (3) apply to all coupled transmitters of the American Marconi Company.
196
PRACTICAL WIRELESS TELEGRAPHY.
168. Plotting of Resonance Curves. — A calibration of the closed and
open circuits of a radio-transmitter is frequently desired to determine, let us say,
the variation of frequency or wave length occasioned by the insertion of a certain
amount of inductance. The results of such measurements are plotted on cross-
section paper in the form of a curve (or perhaps a straight line). The principal
advantage of such plotting lies in the fact that it enables one to take a character-
istic set of readings at two or more decisive points and thus determine interme-
diate values by following the general outline of the curve.
AERIAL TUNING
INDUCTANCE
WATTMETER,
Fig. 217 — Complete Apparatus for Measuring Decrement of Antenna Oscilla-
tions and Plotting a Resonance Curve.
The resonance curve of the radiated wave of a transmitter is a graphic way of showing
the relation between the amplitude of the current and the frequency or wave-lengths at and
near the fundamental frequency. The value of the plotting lies in the fact that it enables
the experimenter to obtain, in a general way, the over-all distribution of energy in the emitted
wave, the decrement of damping and the relative power of the two waves, if present.
To plot the resonance curve of the radiated wave, a wavemeter is required, in series
with which is connected either a hot wire milliammeter or a hot wire wattmeter. The
milliammeter should have a range of, say 40 to 240 milliamperes, while the wattmeter may
have a scale reading of .01 to .1 watt. The latter instrument is preferably connected to the
secondary winding of a step-down transformer, the primary winding of which is connected
PRACTICAL RADIO MEASUREMENTS.
197
in series with the circuit of the wavemeter. This transformer, as a rule, is made up of
Litzendraht wire, the primary consisting of ten turns wound on a wooden spool, about \l/2
inches in length by 1 inches in diameter. The secondary winding consists of five turns of
the same wire wound directly over it with a single layer of empire cloth between.
The wattmeter having been connected in the circuit of the wavemeter, a few preliminary
trials are made to determine the proper inductive relation between the coil of the wavemeter
and the antenna circuit. Care must be taken that the wattmeter is not burned out at the
point of resonance. The proper inductive relation having been obtained by trial, the coil
of the wavemeter is placed in such position as to give a near maximum scale deflection of
the wattmeter at the resonant adjustment for the longer wave. If maximum deflection of
the wattmeter is obtained at resonance, it is evident that the current will decrease at wave-
lengths off resonance, the reduction being dependent upon the decrement of the oscillations.
Readings of the indicating instrument having been observed at resonance, another read-
ing is taken at a point off resonance where the wattmeter shows a small scale deflection, say,
.01 watt. Similar observations are made at other wave lengths approaching resonance and
beyond resonance until a full set of calibrations are secured; that is to say, the observations
are continued to a point beyond resonance where a nearly zero deflection of the wattmeter
is obtained.
A diagram of connections and the relative positions of the apparatus for this de-
termination are shown in Fig. 217, where the closed oscillatory circuit of a radio transmitter
is represented by the
primary winding, the
high potential condenser
and the rotary spark gap.
The antenna system in-
cludes the secondary
winding, the aerial tun-
ing inductance and the
earth wire, which pref-
erably has a single turn
of wire, L-l, inserted in
series. The coil of the
wavemeter, L, is placed
in inductive relation to
L-l and is in series with
the primary winding of
the step-down transform-
er, T, and the variable
condenser, C. The sec-
ondary of this trans-
former is connected to a
low-range radio-fre-
quency wattmeter.
Assume, for example,
that the spark is dis-
charging and that the
closed and open oscilla-
tion circuits are in exact
resonance ; furthermore,
that two positions on the
variable condenser which
we may call C-l and C-2 are the points at which the wavemeter is in resonance with the
double wave. Then, as the pointer of the variable condenser is moved from zero position
toward C-l, the reading of the wattmeter increases, until the point, C-l, is passed, when a
decrease takes place. An increase of current again takes place as C-2 is approached fol-
lowed by a decrease when the point of resonance is passed. If the wave-length of the wave-
meter and the corresponding deflection of the hot wire wattmeter be observed over a series
of wave-lengths, the data thus obtained may be plotted in the form of a resonance curve in
the following manner. . (See Fig. 218).
Placing in one column the wave-lengths corresponding to the condenser scale of the wave-
meter, and in the second column the corresponding deflection of the hot wire wattmeter,
500
800
600 700
WAVE LENGTH
Fig. 218 — Resonance Curve of the Antenna Oscillations.
900
198
PRACTICAL WIRELESS TELEGRAPHY.
co-ordinate points are laid off on cross-section paper through which a common line or curve
is drawn. A typical set of readings follows:
Wave-length of the
wavemeter
450
495
525
535
540
560
575
585
600
615
625
635
655
700..
Corresponding deflection
of the hot wire wattmeter
0.0
0.005
0.01
0.009
0.01
0.03
0.05
0.08
0.1
0.085
0.05
0.03
0.01
..0.00
With the cross-section paper before us, the wave-length readings are laid off horizontally
as indicated in Fig. 218 and are known as the abscissas of the points on the curve, while the
hot wire wattmeter readings are laid off vertically and are known as the ordinates of the
points on the curve. Take, for example, the wave-length of 575 meters ; the corresponding
300
400
500 600 700
WAVE LENGTH IN METERS
800
Fig.
219— Curves Showing the Change in Wave Length by Addition of Inductance in a Radio-Frequency
Circuit.
PRACTICAL RADIO MEASUREMENTS. 199
hot wire wattmeter deflection is .05. Then follow the vertical line corresponding to 575
until the horizontal line is met corresponding to .05 and place a dot or a cross. Proceed
similarly with the entire set of calibrations until all points on the curve are located. Then
draw a line joining them.
Now, if the coil, L, of the wavemeter remains in the same position relative to the coil, L-l,
and the primary and secondary windings of the oscillation transformer, are set at various
couplings, the curve in Fig. 218 will become "sharper" or "broader," accordingly, as the
coupling is decreased or increased. By means of these curves the relative sharpness of the
radiated waves can be compared allowing to some extent a predetermination of the amount
of interference to be expected. If the coupling at the oscillation transformer is properly re-
duced, the lower peak of the radiated wave, which in the curve exists at about 520 meters,
may completely disappear and a single sharp maximum peak result. The resonance curve
shown in Fig. 218 is not that of a "sharp" wave in compliance with the United States restric-
tions, unless the decrement of the antenna current is 0.2 or less per complete oscillation. It
is, however, "pure" as far as the relative amplitudes of the two waves are concerned.
Should the wavemeter indicate no sharp or defined point of resonance, it may be due to an
excess of coupling at the oscillation transformer, to high resistance joints or to poor con-
nections in the antenna circuit. Again, this may lie due to leakage across the antenna
insulators; the remedy, of course, is obvious.
Using the apparatus employed to obtain data for a resonance curve, the student may
obtain data and construct other curves indicating the wave length of the open and closed
oscillatory circuits with various turns of inductance cut in at the primary and secondary
windings. For example, if the increase in wave length brought about by adding turns in the
closed circuit is to be determined, the wavemeter is placed in close inductive relation to the
primary inductance, but not too close to burn out the wattmeter I. Starting with one turn
in the closed circuit, the wave length is determined by observing the wavemeter reading corre-
sponding to maximum deflection of the wattmeter (with spark, of course, discharging).
Turns are then added progressively at the secondary (from one to maximum) until a com-
plete set of calibrations are obtained. The results of a typical set of calibrations follow :
Corresponding wave-
Turns lengths in meters
1 404
2 416
3 428
4 444
5 458
6 472
7 482
8 488
9 495
10 505
11 514
12 528
Plotted in curve form these data appear in curve A, Fig. 219. Here the wave-lengths (in
meters) are the abscissas of the points on the curve and the helix' turns the ordinates of the
points on the curve. The wave lengths corresponding to fractions of a turn on the helix
can be determined by following the abscissae to the base line or the horizontal axis.
We can plot the calibrations of the open circuit of a transmitting system in a similar way,
but in this case a spark gap must be connected in series with the antenna system and in turn
connected to the secondary winding of an induction coil. Generally the oscillations flowing
in the antenna circuit are not powerful enough with this connection to operate the wattmeter
(in series with the wavemeter), or the spark discharge of the coil may be too irregular to
permit a reading of the wattmeter to be observed. It is therefore preferable to shunt the
wavemeter by a crystalline detector and head telephone, the point of resonance being located
by the maximum sound in the receiver.
Turns are added in the antenna circuit one at a time and corresponding wave length
readings observed on the wavemeter. A typical set of readings follows :
200 PRACTICAL WIRELESS TELEGRAPHY.
Corresponding wave-
Turns lengths in meters
1 290
2 410
3 525
4 600
5 683
6 770
These data appear in the curve, B, Fig. 219. Intermediate wave lengths lying between the
complete turns may be found as in the previous case.
Curves of the latter type should be prepared at each commercial station and posted in the
apparatus room for quick reference. In this manner, the open and closed oscillatory circuits
may be tuned to the standard waves with the assurance that the circuits are in exact
resonance.
Returning to the resonance curve of Fig. 218 : Assume that the portion of the curve, Fig.
218, above the horizontal line marked .05 represents the range of wave lengths over which
the signals are audible at a receiving station located, say, 75 miles distant from the
transmitter.
It is easily seen that a change of 20 meters on either side of the maximum ordinate will
reduce the incoming signals to zero. It is also plain that the sharper the curve, the greater
will be the reduction of the strength of the incoming signal for a given amount of detuning
at the receiver. Hence resonance curves, in a sense, enable us to determine the ratio of the
current at the receiver for a given wave length off resonance to that obtained at the maxi-
mum ordinate or resonance.
169. Measurement of the Logarithmic Decrement of Damping. — The de-
termination of the decrement of damping of the antenna oscillations is a measure
of the tuning qualities of a radio-transmitter and, in a sense, permits a prede-
termination of the interference to be expected therefrom. If the decrement of the
oscillations flowing in the open circuit is known, we may determine the number
of oscillations per spark discharge as follows :
4.605 + 8
M=- (1)
8
where 8 = Naperian logarithm of the ratio of two successive oscillations
in the same direction ;
M = number of complete oscillations in the train when the last one
has attained amplitude of .01 of the initial oscillation.
Hence if the emitted wave has a decrement of 0.2 there will be approximately 24
complete oscillations per spark.
It has been determined by experiment that a transmitter having decrement in excess of .2
per complete oscillation causes excessive interference to the operation of other stations not
tuned to the same wave length, and it necessarily follows that the greater the decrement of
the radiated wave the greater will be the interference, e. g., the wave will lack tuning quali-
ties. Hence, as far as tuning and the elimination of interference is concerned, it is desirable
to keep the decrement at a minimum value.
Modern quenched spark transmitters have oscillation decrements lying between .05 and .12
and therefore set up a minimum of interference, to the operation of other stations.
It has been shown by V. Bjerknes that the combined decrement of two circuits of radio-
frequency, magnetically coupled, is given by the following formula:
(Xi \ r
i -- |V
Xr /
(2)
I'2
Where (in the case where a wavemeter is coupled to the antenna system of a wireless tele-
graph transmitter),
*Some writers express the logarithmic decrement on the basis that the amplitude of the last oscillation
is one-tenth of the initial oscillation.
PRACTICAL RADIO MEASUREMENTS.
201
5i — decrement of the circuit under measurement,
&j =: decrement of the decremeter or wavemeter,
\r = wave length at resonance,
Xi = wave length not more than 3 per cent, to 5 per cent, off resonance,
1J =: current indicated by a measuring instrument connected in series with the
wavemeter when the wavemeter is adjusted to Xt.
I rs — current indicated as above when the wavemeter is adjusted to resonance.
For accuracy 52 must be small as compared with Si.
In terms of the condenser capacity of the wavemeter, the foregoing formula can be written
as follows.
C' — O
5i 4- S3 =
(3)
Where Cr = capacity of the wavemeter condenser at resonance;
G =: capacity of the wavemeter condenser of a certain point off resonance.
It has been found for all practical purposes, that if the value of I' is selected to be one-
half the value of I"-", the formula is sufficiently accurate; hence, the integers underneath
Fig. 220 — The American Marconi Company's Decremeter.
the radical may be cancelled and the combined and total decrement of the two circuits obtain
from the following simple formula:
Cr — G
Cr
(4)
Now, it is found by experiment that the resonance curve of a radio-transmitter is not
always symmetrical and, therefore, different values for the decrement will be found accord-
ingly as the measurement is made on either side of the maximum ordinate. Consequently the
results will be more accurate if the capacity of the condenser is taken above and below
resonance at points where the corresponding flow of current as measured by the wattmeter
is one-half the value obtained at resonance; then the mean value of the decrement will be
determined as follows :
202
PRACTICAL WIRELESS TELEGRAPHY.
— Ci TT
-f «• — -
(5)
where Cs — the capacity of the condenser at a value greater than C«-, the capacity
where the reading of the wattmeter falls to one-half that
obtained at Cr and,
Q = the capacity of the condenser at a similar wattmeter reading corre-
sponding to a capacity less than Cr.
Although the logarithmic decrement of a transmitter may he measured by several methods,
but one considered the most practical by U. S. engineers will be described.
To carry out this measurement, a wavcmcter fitted with a current indicating instrument
is required, which may be either a hot wire milliammeter or a hot wire wattmeter. The con-
denser of the wavemeter should have a chart showing the capacity in microfarads corre-
sponding to each position of the pointer on the condenser scale and the hot wire wattmeter
should have a range of .01 to .1 watts.
To measure the decrement, the wattmeter should be connected as in Fig. 217 for obtaining
the data for plotting a resonance curve.
The coil, L, of the wavemeter is then placed in inductive relation to the antenna system
Fig. 221 — Kolster Decremeter — the Type Used by the Government Radio Inspectors.
at the single turn of wire, L-l. The key of the transmitting apparatus is held down con-
tinuously and the length of the spark gap adjusted until the note is clear and uniform. This
is followed by variation of capacity of the wavemeter condenser until the wattmeter indictes
a maximum deflection which, of course, is obtained at the point of resonance
between the two circuits. The inductance coil L is then moved about — that is to say — the
coupling between it and the antenna coil L-l is changed until the maximum reading of the
wattmeter falls (as a matter of convenience) on some even number, say 0.08 watt. The
condenser is then set at a lower value of capacity, O, where the reading of the
wattmeter is 0.04 watt. A value of capacity above Cr is then observed (Cs) where the
PRACTICAL RADIO MEASUREMENTS.
203
reading of the wattmeter again falls to 0.04 watt. Substituting these values of capacity in
formula No. 4 the combined decrement of the two circuits is obtained by a simple calculation.
Now, if the decrement of the wavemeter is subtracted from the total value obtained by
the last equation, the result will be the decrement of the radiated wave. The decrement of
the wavemeter can be obtained by direct calculation or by actual measurement.
170. Calculation of the Decrement of the Wavemeter (or Decremeter). —
One method by which the damping' of the wavemeter may he determined is car-
ried out as follows:
After the value of 81 _|- 82 is obtained, the coupling between the wavemeter coil and the
antenna system must not be altered. A piece of resistance wire, R (Fig. 217), is stretched
tightly between two binding posts and connected in series with the circuit of the wavemeter.
The amount of wire in use is gauged by the sliding contact, T-l. (A piece of No. 28 German
silver wire or Tberlo wire about 15 inches in length will be found satisfactory.)
With the pointer of the condenser set at Cr, or resonance, the spark gap is energized and
resistance added at R until the reading of the wattmeter falls to exactly one-half that
obtained in the original resonance adjustment, or 0.04 watt. The condenser of the wave-
meter is then shifted to either side of resonance to such a value of capacity that will give
^ggj
Fig. 222 — Rear View of Kolster Decremeter.
one-half the wattmeter reading obtained at Cr, viz., 0.02 watt. Let the capa'city of the wave-
meter condenser below resonance by represented by C3 and the capacity above resonance by
C«. Then the following formula is applicable :
_|_ 82 _j- 5s —
X 1.57
(6)
Now, 8S is the decrement due to the addition of the resistance R, and it is evident that if
the value of 81 -|- 82 is subtracted from 81 _}_ Sa _|_ Sa, the value of & is at once obtained.
It has been shown by Fleming and others that if the value of 82 is thus found out, we may
evaluate the decrement of the wavemeter 82 by the following formula :
Letting V stand for the value obtained in equation No. 5 and Vi for the value in No. 6,
then,
V1 X 5s
*=- (?)
2V — Vi
204
PRACTICAL WIRELESS TELEGRAPHY.
Hence, by subtracting the value of 82 from 5i -j- 6-2 We have 5i, the decrement of the aerial
circuit under test.
Assume for example,
and
52
-f- 52 = 0.15
_j_ 5a=0.17
thenSs = 0.02
0.17
and 5s = —
X 0.02
= 0.026
0.30 — 0.17
therefore Si =0.15 — 0.026 = 0.124
If a milliammeter is connected directly in series with the wavemeter or decremeter, in
1
place of the wattmeter, the reading of the meter at the point off resonance should be -
1.41
of that obtained at resonance or approximately 71 per cent.
A resonance curve of the antenna oscillations, having been taken for any reason whatever,
may be used for calculation of the decrement, for it is apparent that the data required for
formula No. 5 is included in such curves.
If the variable condenser of the wavemeter is constructed so that the capacity varies
directly with the scale reading, the actual capacity of the condenser need not be known.
The reading of the condenser scale for the points on and off resonance can be substituted in
formula No. 5 in place of the condenser capacity and the decrement measurement carried on
as usual.
Formula No. 2 can be written :
\2 — X.
Si -f 52 =r
3.1416
Xr
(8)
where Xr = wave length at resonance ;
1 1 - — current corresponding thereto in the circuit of the wavemeter;
X2 ~ wave length 3 per cent to 5 per cent, above resonance ;
Xi — wave length 3 per cent, to 5 per cent, below resonance ;
I2 = current corresponding to wave lengths above and below resonance.
The decrement of the wavemeter must, of course, be subtracted to obtain the value of Si.
Direct reading decremeters, such as the Kolster* decremeter (U. S. Bureau of Standards)
are in use. In this instrument, a dial geared to the movable plates of the variable condenser
is fitted with a scale of
decrements and when the
reading of the wattmeter
at a given point off
resonance is one-halt
of that obtained at reson-
«ince, the combined decre-
ment of the decremeter
and the circuit under
measurement is obtained
by first setting the decre-
ment scale at zero (when
one-half resonance cur-
rent is obtained) after
which the decrement dial
is clamped to the movable
plates of the variable
condenser and the latter
turned to resonance and
to a point beyond where
the reading of the watt-
meter again falls to one-
Fig. 223 — Wavemeter as a Source of Radio Frequency Oscillations.
'Bureau of Standards publication No. 235 describes the Kolster Decremeter in detail.
PRACTICAL RADIO MEASUREMENTS.
205
half that at resonance. The decrement dial will then indicate the combined decrement of the
circuit under measurement and that of the decremeter.
A photograph of the Marconi decremeter appears in Fig. 220 and the Kolster decremeter
in Figs. 221 and 222. The latter is used by all U. S. Government radio inspectors.
171. Wavemeter as a Source of High Frequency Oscillations. — A wave-
meter excited by an ordinary vibrating buzzer may be used to generate feeble
oscillations of radio-frequency for measuring purposes.
The complete diagram for the apparatus is shown in Fig. 223. The circuit from the
battery to the buzzer B-l is completed through the coil of the wavemeter L. To eliminate
sparking at the vibrator, the windings (of the buzzer) are shunted by a non-inductive re-
sistance of 100 ohms or by a condenser of 1 mfd. capacity.
When the buzzer is put in action, a change in the lines of force threading through L
takes place and the condenser C receives a charge, which afterward discharges through L
1
at a frequency corresponding to — — Since the capacity of C is variable, oscillations of
V L C '
various frequencies may be generated and caused to act inductively on another circuit of
radio-frequency for whatever purpose required.
Fig. 224 — Station Type Wavemeter of the American Marconi Company, Showing Exploring Coil, Thermo-
couple and Galvanometer.
172. Calibration of the Secondary and Primary Circuits of a Receiving
Tuner. — The secondary circuit of a receiving tuner can be calibrated in
terms of wave length by the method shown in Fig. 223, wherein the secondary
winding of a tuner is indicated at L-l, the shunt variable condenser at C-l, the
detector at D, and the telephone at P.
A certain value of inductance and capacity are selected at L-l and C-l respectively,
followed by setting the buzzer into vibration. With the wavemeter in inductive relation, the
capacity of the wavemeter condenser is varied until a maximum of sound is heard at tele-
phone P. The wave length of the secondary circuit is then identical with the setting of the
wavemeter.
206
PRACTICAL WIRELESS TELEGRAPHY.
Other values of inductance may be selected at L-l, the capacity of C-l varied progressively
from zero to maximum, and the corresponding wave length measured by the wavemeter.
These calibrations may be plotted in curve form on cross-section paper or in the form of a
table for ready reference.
The open circuit of a receiving station can be calibrated by the method shown in Fig.
213. With the buzzer in operation, inductance is progressively added at the aerial tuning
inductance L-2 or the primary winding L-l of the receiving transformer, and the wave
length reading observed at the wavemeter. The reduction of wave length occasioned by the
short wave condenser may be measured on the wavemeter in the same manner.
If, during the preliminary adjustment, resonant response cannot be secured by this method,
it indicates that the wavemeter has not the proper range for the tuner. Hence, some knowl-
edge of the probable wave length of the circuit should be obtained before undertaking the
test and a fitting wavemeter supplied. The wave length can be roughly estimated from the
approximate values of inductance and capacity in the circuit.
Buzzer- Tester ~==
Fig. 225 — Showing How Open and Closed Oscillation Circuits of a Receiving Tuner May Be
Calibrated.
173. Calibration of the Open and Closed Circuits Simultaneously. — The
most satisfactory method of calibrating a receiving tuner or adjusting the re-
ceiving system to a standard wave length with a given aerial, is to place a wave-
meter in inductive relation to the antenna at all times as in Fig. 225.
Since a change of coupling changes the tuning of the open and closed circuits, the exact
adjustment of the circuits for the loudest response with any degree of coupling can be de-
termined by setting the wavemeter into excitation and causing it to act inductively upon the
open circuit. This should be followed by variation of the inductance and capacity in both
the open and closed circuits until a sharp maximum is obtained in the head telephones of the
receiver. The loudest response, of course, is secured when the wavemeter, the closed, and
the open circuit are all in electrical resonance. At the same time, the crystal rectifier can
be adjusted to maximum sensitiveness.
Care should be taken, during this calibration, to vary the values of inductance and capacity
PRACTICAL RADIO MEASUREMENTS.
207
of the closed and open
circuits in a progressive
manner, e. g., an increase
of inductance in the an-
tenna circuit calls for a
corresponding increase
in the closed or detector
circuit, or vice versa.
Using solid rectify-
ing detectors, the in-
ductance of the wave-
meter can only be placed
an inch or so from the
earth lead, but with a
sensitive vacuum valve
amplifier, the wave-
meter may be placed
several feet from that
lead.
L WAVEMETER
Fig. 22£ — The Measurement of the Natural Wave Length of a Simple
Tuning Coil.
174. Measurement of the Natural Oscillating Period of a Coil. — The
natural wave length of a tuning coil, as a simple open circuit oscillator, may be
measured by the circuit and apparatus shown in Fig. 226.
The radio-frequency coil A, B, is set into excitation by an aperiodic buzzer circuit which
includes the 1 mfd. condenser C-l and the resistance R. of 2,000 ohms. The wavemeter, fitted
with a sensitive detector
D, is placed in inductive
relation to the coil in the
usual manner. If the
coil possesses a fair
value of distributed ca-
pacity, the resonant point
on the wavemeter will
be sharply defined, but,
lacking this, the point of
resonance may be some-
what difficult to locate.
175. Measurement
of Electrostatic Ca-
pacity.— (a) Capac-
ity at low voltage and
audio-frequencies. We
may measure the sim-
ple electrostatic ca-
pacity of a condenser
or an aerial by the
bridge method of Fig.
227. The condenser
of unknown capacity
is shown at C-x, and
a standard variable
condenser calibrated
in microfarads at C-n.
R-l and R-2 are non-
inductive resistances
of low value such as
found in the usual
sliding .wire bridge. P rig. 227— Diagram
Electrostatic Capacity.
208
PRACTICAL WIRELESS TELEGRAPHY.
and S are the primary and secondary windings respectively of an ordinary tele-
phone induction coil. A vibrating buzzer is indicated at B-l, and the battery at
B-2. This apparatus affords a source of electromotive force for obtaining balance
of the bridge.
To carry out the measurement, the buzzer is set into vibration and the values of R-l and
R-2. varied until complete silence or a minimum of sound is heard in the telephone P-l. The
various quantities are then related as folows :
C-x R-2 R-2
= or C-x = X C-n
C-n R-l R-l
If condensers C-x and C-n have different dielectrics, complete silence cannot be obtained,
hence a minimum of sound is an indication of balance. To carry out the measurement for
low values. of capacity, the total resistance of the sliding wire bridge, need not exceed 110 ohms.
If the aerial and earth
wire of an antenna sys-
tem be substituted for the
condenser C-x, its elec-
trostatic capacity may
thus be determined, but
it should be borne in
mind that the simple
electrostatic capacity of
an aerial and its "ef-
fective" capacity when
traversed by alternating
current of radio-fre-
quency are of different
value. This is due to the
non-uniform distribution
Fig. 228— Measurement of Electrostatic Capacity at Radio Frequencies. JJ* cu™"ent and voltage
throughout the open cir-
cuit which causes the capacity to vary with the applied frequency. Generally the effective
capacity is less than the simple electrostatic capacity. (The latter value is the capacity
obtained by considering the aerial merely as one plate of a condenser, the earth the opposite
plate and with uniform current and voltage distribution.)
A standard of capacity for the bridge may be constructed from flat brass
plates, of rectangular form and its capacity may be calculated by the following
formula :
A
C = - mfds.
47r T 900,000
where A = area in sq. cms. of the dielectric covered by the plates,
T = separation of the plates in cms.
(b) Measurement of Capacity at Radio-Frequencies. The capacity of the
condensers used in receiving circuits may be determined by the method shown in
diagram of Fig. 228. A wavemeter L, C (or any variable condenser and induct-
ance within the required range) is set into excitation by the buzzer B-2. The
resulting oscillations are caused to
act upon the second circuit of vari-
able frequency, L-l, C-x or L-l,
C-n. C-n is a standard variable con-
denser calibrated in microfarads,
and C-x the condenser, the capacity
of which is to be determined. A
crystal rectifier connected uni-later-
ally at D is shunted by the telephone
P. A double pole double throw
switch permits either condenser to
rig. 229 — Measurement of Capacity by Means of a i j • j. ,1
Wavemeter. be connected into cri
PRACTICAL RADIO MEASUREMENTS. 209
With the huzzer in vibration, inductance L-l is varied until resonant response is obtained
in the telephone or when L, C := L-l, C-x. The D. P. D. T. switch is then thrown to C-n,
and its capacity altered until circuit L-l, C-n, is again in resonance with L, C. Obviously,
the capacity of C-x is that of C-n, which is already known.
For accuracy, the coupling between L and L-l should be reduced to a degree consistent
with the strength of signals. To bring the two circuits in resonance, it may be necessary
with certain condensers to vary the capacity of C.
Another method for quickly determining the capacity of a condenser is shown in Fig. 229.
A standard wavemeter, L, C-n, has the condenser of known capacity C-n and the crystal
rectifier D connected unilaterally. The wavemeter is tuned to resonance with any spark
transmitter such as L-l, C-l, S-l, and the capacity of C-n noted. With the spark still dis-
charging at S-l, C-x is connected in shunt to C-n and the capacity of C-n reduced until
resonance is obtained again. For example, if the capacity of C-n in the first measurement is
.007 mfds., and in the second test, .002 mfds., the capacity of C-x must be the difference of the
two readings, or .005 mfds. Circuit L-l, C-l, S-l may be replaced by a wavemeter and buzzer.
176. Measurement of the Effective Inductance of a Coil at Radio
Frequencies. — The effective inductance of a given coil can be determined by
the connections and arrangement of apparatus in Fig. 228. Assume that the in-
ductance of L-l is required and condenser C-n is connected in shunt; then L, C,
and L-l, C-n, are tuned to resonance with very loose coupling. Then if L.C, is a
standard wavemeter, the wave length of L-l, C-n is at once obtained. Then,
A2
3,552 X C-n
where L = the inductance of the coil in centimeters.
177. Calculation of Inductance from the Constants of the Coil.*— The
Nagaoka formula for calculating the inductance of a single layered coil is
expressed as follows : ^ ns
L = 4 »* - K,
b
where L = inductance in centimeters,
a = mean radius of coil in centimeters,
n = total number of turns,
b = length of coil in centimeters,
2 a
K = a constant varying as the ratio - .
2a b
Values of K for — appears in the curves of Fig. 230.
b
If the dimensions of the coil are given in inches, the student can convert them to centi-
meters by multiplying by 2.54 (1 inch = 2.54 centimeters). Also the radius is one-half the
2a
diameter, hence the ratio of — is readily obtained, and the corresponding value of K from the
b
2a
curve. Thus if — = 1.35, then K = 0.84.
b
(a) Example 1. — Assume a coil of 10 turns with mean diameter of 18 inches, and overall
length including the insulation (if any) of 12.5 inches. The inductance is calculated as follows :
n = 10 turns ;
b = 31.75 centimeters;
a = 22.9 centimeters ;
2a 18
= 1.44 and from Fig. 230 K = 0.826.
b 12.5
(22.9) 3 X (10)*
Therefore L = 4** --- - X 0.826 or 53,825 centimeters.
31.75
'Presented by Wm. II. Priess in the August, 1915, issue of the Wireless Age.
210
PRACTICAL WIRELESS TELEGRAPHY.
PRACTICAL RADIO MEASUREMENTS.
211
(&) Example 2.— Calculate the inductance of a coil three inches in diameter, 8 inches in
length, wound closely with No. 26 double silk-covered wire. From the table on page 213 the.
diameter of No. 26 D. S. C. wire is .02014 inches, hence,
8
= 397 turns ;
0.02014
b — 20.3 centimeters ;
a = 3.81 centimeters.
2a
_ — 3/8 — 0.375, and from Fig. 196
b
K = 0.859
(3.81 r X (397) 2
Therefore L = 4ir - - x 0.859, or 3,820,000 centimeters.
20.3
i.oo
09O
O IQ
0 00
O6 04 Oi oo^Oi 04- 06 03 10 li 14 16 18 20
Fig. 231 — Curves Showing the Value of a Constant for the Ratio of the Diat
lHf«1W*"ff»~'yir"y.i ^ 3.4
eter of a Wire to Its Pitch.
In the curves of Fig. 230, values of K are given for coils lying between those of infinite
length and those where the diameter is 9l/2 times the length. This covers all conditions
encountered in practice.
(c~) Correction factor. — For practical calculation the foregoing formula is sufficiently
accurate, but for greater precision a correction factor must be applied. 'In fact, the inductance
values obtained in examples 1 and 2 are termed the ''current sheet'' inductance, based upon
the assumption of a coil wound with infinitely thin tape, the turns of which are assumed to
touch but not to be in electrical contact.
Dr. Rosa of the Bureau of Standards has given an expression for circular sectioned non-
magnetic wire as follows : If the true inductance is designated as L, and the current sheet
inductance as L-s, then,
L = L-s — L-c
where L-c is the correction value, and,
L-c — 4^r a n (K-> -f K»)
where Ka and K? are constants of the coil. (See B of S vol 8, pp 197 and 199)
d
Now K* is a constant plotted to the parameter of — which is the ratio of the diameter
PRACTICAL WIRELESS TELEGRAPHY.
COO 0-
Fig. 232— Showing the Values of
1.0 0.15 O2.0 0-25 0.30
a Correction Factor for Determining the True Inductance of a Coil
PRACTICAL RADIO MEASUREMENTS.
213
of bare wire to its pitch in a given winding and for any given value of — a value of Ka
D
appears in Ing. 231, It should be noted that Kz may be positive, negative or zero; that is,
on the left of the zero line Ka is positive and on the right hand side negative.
Ka is another factor plotted against the number of turns in the coil as in Fig. 232 where
it will be seen that Ks is zeio for one turn and 0.3365 for 1,000 turns.
(d) Corrections for Example 1. — We shall now calculate the value of L-c for example 1.
d
Assuming the wire of the helix to have a diameter of *4 inches with spacing of one inch, —
.250
1)
— .025 and from the curve, Fig. 231, Ka — — 0.8 (of negative value).
1.000
Since N — 10, then from the curve, Fig. 232, Ka = 0.266, hence,
L-c = 4*- x 22.9 X 10 (—0.8 + 0.266),
L-c = 12.566 X 22.9 X 10 (—0.534) cms.
hence L-c = — 1,540 cms.
and L = 53,825 — (—1,540) = 55,365 cms.
(e) Correction for Example 2. — The diameter of bare No. 26 B. and S. wire is .01790
inches and of D. S. C. No. 26, .02014 inches, hence,
d .01790
— = = 0.889
D .02014
From Ka curve, Ka = -fO.441 and since n = 397, therefore Ka = 0.335 approx.
Therefore L-c = 4* X 3.81 X 397 (0.441 + 0.335) cms.
L-c — 14,750 cms.
L = 3,820,000 — 14,750 = 3,805,250 cms.
L-c
and — = 0.38 per cent, the correction factor.
L •
The correction factor is thus quite appreciable for some coils and rather negligible for
others. With currents of radio-frequency there is an altered current distribution in the con-
ductor which affects the inductance, giving a lesser value than in circuits where the current
is uniformly distributed throughout, but the finer the wire, the smaller will be the change of
inductance due to increase of frequency.
A table of the diameter of various sized wires in the B. and S. gauge follows :
TABLE NO. 1.
Silk and Cotton-Covered Annealed Copper Wire.
Diameter in Mils.
B.&S.
Single
Double
Single
Double
Gauge
Bare
Cotton
Cotton
Silk
Silk
20
31.961
37.861
42.161
34.261
36.161
21
28.462
34.362
38.662
30.762
32.662
22
25.347
31.247
35.547
27.647
29.547
23
22.571
28.471
32.771
24.871
26.771
24
20.100
26.000
30.300
22.401
24.300
25
17.900
23.800
28.100
20.200
22.100
26
15.940
21.840
26.140
18.240
20.140
27
14.195
20.095
24.395
16.495
18.395
28
12.641
18.541
22.841
14.941
16.841
29
11.257
17.157
21.457
13.557
15.457
30
10.025
15.925
20.225
12.325
14.225
31
8.928
14.828
19.128
11.228
13.128
32
7.950
13.850
18.150
10.250
12.150
33
7.080
12980
.17.280
9.380
11.280
34
6.304
12.204
16.504
8.504
10.504
35
5.614
11.514
15.841
7.914
9.814
36
5.000
10.900
15.200
7.300
9.200
37
4.453
10.353
14.653
6.753
8.653
38
3.965
9.865
14.165
6.265
8.165
39
3.531
9.431
13.731
5.831
7.731
40
3.144
9.044
13.344
5.344
7.344
214
PRACTICAL WIRELESS TELEGRAPHY.
This data is essential in the calculation of the inductance of the coils in radio-frequency
circuits, particularly the tuning coils of the receiving apparatus. Knowing the length of
the winding and the diameter of the wire,
the total number of turns is obtained in
dividing the former by the latter. Multi-
plying this by the circumference of the
coil, the number of feet of wire required
for a given winding is at once obtained.
178. Measurement of the Ef-
fective Inductance and Capacity
of an Aerial. — To measure the ef-
fective inductance of an aerial, a
standard wavemeter and a standard
of inductance is required. The latter
can be made up of Litzendraht wire
and calculated from the inductance
formula in the foregoing paragraph.
The aerial is set into excitation by an
induction coil or transformer S, Fig. 233,
and the wavemeter placed in inductive
relation. The reading of the natural wave
length thus obtained may be designated as
Xi. We next insert the standard induct-
ance L1 and take a second reading of the
wave length which may be designated
by Xs.
PHONES
Fig. 233 — Diagram of Connections for Measuring the
Inductance and Capacity of an Aerial.
then L = - $ —
(\22 — X!2)
where L = inductance of the aerial in microhenries ;
L1 — inductance of the standard in microhenries.
To determine the effective capacity of an aerial, first measure the natural wave length Xi
then insert a condenser C1 of .001 microfarads capacity and take a second measurement of
wave length X2. Obviously X2 is less than Xi. Then the capacity
—
—
Xi2
where C = capacity of the aerial in microfarads.
179. Calibration of a Wavemeter from a Standard. — If a calibrated wave-
meter can be procured, the wave-
meter described at the beginning of
this chapter can be calibrated from
it in a simple manner, as shown in
Fig. 234.
tively, are
Here, L and C respec-
the inductance coil and
condenser of a standard wavemeter
which is set into excitation by the
buzzer, H, and the batteries B. The
winding of the magnets of the
buzzer are shunted by a condenser
K, of about 1 microfarad capacity,
for which may be substituted, if
desired, a non-inductive resistance
of about 100 ohms. These are in-
tended to absorb the counter electromotive force of the buzzer winding.
When the buzzer is set into operation, the wavemeter L C becomes a miniature trans-
mitting set, radiating waves corresponding to a definite frequency of oscillation which will
be recorded on the wavemeter L-l, C-l, when it is in resonance with L, C. The standard
Fig. 234— Simple
Method of Calibrating
from a Standard.
Wavemeter
PRACTICAL RADIO MEASUREMENTS.
215
wavemeter L, C is then set at various wave lengths and the buzzer put into operation, being
carefully adjusted for clear tones. The capacity of the condenser C-l, is then altered until
a maximum of sound is heard in the head telephones. Obviously, L-l, C-l has the same
wave length as L, C, and a record of the setting is made accordingly. Thus if six or eight
readings are taken, covering the entire scale of C-l, the data can be plotted on cross-section
paper in the form of a curve. Intermediate values of wave lengths are readily determined
from the curve.
For accuracy during calibration, the degree of coupling between L and L-l must be kept
as low as is consistent with the strength of signals. If response is not secured readily at
the wavemeter, L-l, C-l, it may be that the values of inductance and capacity are such that
the circuit is out of resonance with the standard wavemeter L, C. If so, different values
of inductance or capacity must be selected until a resonant response is secured. It is not
necessary for the crystal rectifier, shown in Fig. 234, to be connected unilaterally to the
wavemeter. It may be shunted around the circuit as in the usual receiving set.
Fig. 235 — Three Way Calibration of Wavemeter for Greater Accuracy.
To eliminate all possibility of error in calibration due to the added capacity effect of the
shunt excitation circuit of the foregoing connection, a three-way method may be employed
as shown in Fig. 235. Herein, B is an accurately calibrated standard wavemeter with a
crystal detector and head telephones connected unilaterally. The wavemeter under calibra-
tion is represented at C and also has a detector connected unilaterally. At A are the circuits
comprising the fixed inductance L, the condenser C, the buzzer B, the battery Bat, and the
shunt condenser. By means of the calibration chart furnished with the wavemeter B, the
condenser C-l can be set at any wave length within the range of the meter.
The buzzer having been put into operation, the capacity of the variable condenser of tb'
oscillation circuit, A, is changed until maximum response is secured at the head telephones
of the wavemeter B. During this operation the coupling between the coils, L and L-l, should
be as loose as is consistent with the strength of signals in the head telephones. The point of
resonance having been determined, the coil L-2, of the wavemeter, C, is placed in inductive
relation to L. The capacity of the condenser, C-2, is then altered until a resonant response
is secured in the head telephones. Obviously, the wave length of the wavemeter C, is now
identical with that of the wavemeter B.
216
PRACTICAL WIRELESS TELEGRAPHY.
This process is repeated until a complete set of calibrations are obtained. If desjred,
the crystalline detectors connected to the wavemeters, B and C, may be connected in series
with the head telephone and then in shunt to the condenser. The connection shown, how-
ever, affords greater accuracy because the calibration of the wavemeter is not so seriously
affected.
180. Measurement of Mutual Inductance at Radio /Frequencies. — As-
sume that two coils such as the primary and secondary windings of a receiving
tuner, L-2 and L-3, Fig. 236, are in
inductive relation and the mutual in-
ductance is required.
With the binding posts A, B and C, D
connected together by a jumper, the
C-i wavemeter is tuned to resonance with the
spark gap circuit, L, C, S. The capacity
of the wavemeter condenser C-l is ob-
served and may be designated as C-2.
Inductances L-2 and L-3 are now con-
nected in series and a new value of C-l
obtained for resonance, designated as
Fig. 236— Showing the Connections for Measuring C~3' Then. when the magnetic fields of
the Mutual Inductance of Two Coils at the two coils are in the same direction,
Radio Frequencies. a jarge yalue Qf inductance is obtained
which is equal to L-2 -f- L-3 -f- 2M, and in terms of the two condenser capacities observed
on the wavemeter,
L-2 -f L-3 -f 2M -
L-l
where L-l = inductance of the wavemeter in microhenries.
After this value is obtained, the connections from L-3 to C, D are reversed (as shown
by the dotted lines) and the measurement gone through again. Then if this is the smaller
value of inductance,
C-2
L-2 + L-3 — 2M = I 1 \ L-l
- 2M = (
V C-4
Where C-4 = capacity of the condenser at resonance with the connections to
C, D reversed.
The two values of inductance having thus been obtained, the mutual inductance
L-5 — L-6
M =
4
Where M = the mutual inductance in microhenries ;
L-5 = larger value of total inductance ;
L-6 = smaller value of total inductance.
181. Comparative Measurement of the Strength of Incoming Signals.—
The human ear is not to be relied upon to judge the strength of incoming signals
at a given receiving station when they vary in intensity by values less than 25
per cent. an$ since the comparison of the signals from one or more transmitting
stations is often desirable for purposes of record or adjustment, more accurate
means must be provided. -
The ideal way to measure the strength of the incoming signals would be to place a
galvanometer in the receiver circuits, but this is not feasible, particularly when
the receiving station is far distant from the transmitter or in case discharges of
atmospheric electricity are rather severe. Hence the measurement is carried out by means
of a calibrated shunt resistance connected across the receiving telephone.
The measurement of the signal intensity is carried out as follows : A given transmitter
is tuned to maximum strength of signals at the receiver, followed by connecting a variable
resistance across the telephones, the resistance being reduced until the signals just disappear
or are barely audible.
If we designate the value of the telephone current in microamperes required to make
the least audible signal as C-a, it has been shown that
PRACTICAL RADIO MEASUREMENTS.
217
R + T
C=- -XC-a
R
where C = current in the telephone without the shunt ;
R = resistance of the shunt for the least audible signal ;
T = resistance of the telephone.
Now the value of C-a for the least audible
signal varies with the frequency of the
current flowing through the telephone, the
impedance of its windings, and the sensi-
tiveness of the human ear to weak sounds.
Hence at a given station the value of C-a
is ignored and the strength of the signal
spoken of as being so many times audi-
bility.
Thus as in the diagram, Fig. 237, if
the value of R for the least audible signal
is 50 ohms, and the resistance of the tele-
phone 2,000 ohms, then
2,000 + 50
C = - - C-a = 41, C-a, e. g.,
tt
/wvwwvv —
50
Fig. 237 — Fundamental Circuit of the Audibility
Meter.
the signal is 41 times that required to make
an audible sound in the telephone.
It is clear that the results obtained by this method vary at each station according to the
type of apparatus and the keenness of the observer, hence the audibility factor cannot be
used at two different receiving stations to compare the effectiveness of a given transmitter.
It does, however, permit an approximation which is superior to mere guesswork.
Fig. 238 — Audibility Meter (American Marconi Company).
Shunt resistance boxes are manufactured for this purpose and are termed audibility^ meters.
The resistance coil is fitted with a multipoint switch and the contact studs calibrated in terms
of the audibility of the received signals as compared to the current corresponding to the
least audible signal with the particular telephone supplied with the meter. The type manu-
factured by the Marconi Company of America is shown in Fig. 238.
218
PRACTICAL WIRELESS TELEGRAPHY.
A typical chart* of the relative strength of signals received at different hours
of the day from the Marconi station at Ketchikan, Alaska, at the receiving
station at Astoria, Ore., is shown in Fig. 239. These readings were taken on a
Marconi audibility meter.
*Curve A, Fig. 239, shows the signal audibility throughout the 24 hours of the day from Ketchikan
to Astoria. Curve S shows the intensity of atmospheric electricity. It is interesting to note the distinct
rise in both the signal and "static" intensity near to midnight and the distinct drop during the early
npurs ot the morning. The rise of the peak is found to occur at approximately the same hour in
observations taken over several months duration.
PRACTICAL RADIO MEASUREMENTS,
219
o.i
300
400
&OQ
900
500 600 70Q
WAVE LENGTH IN METERS
Fig. 240 — Curves Showing the Effect on the Radiated Wave By Progressive Reduction of the Coupling
at the Oscillation Transformer.
182. "Tight" and "Loose" Coupling. — The adjustment of the coupling of
a transformer is important because if the primary and secondary of the oscillation trans-
former are closely coupled, oscillations of two frequencies occur in the antenna circuit
as shown by the curve A, Fig-. 240. If the coupling be reduced (by drawing the primary
and secondary windings apart) and a second resonance curve obtained, the two frequencies
tend to merge into one as shown by curve B, Fig. 240. Further reduction of coupling
brings about the condition shown by curve C in which the energy radiated is confined to
practically a single frequency of oscillation. The wave C may be of greater or lesser
amplitude than waves A and B, according to conditions.
Fig. 241 — Showing How Loose Coupling Can Be
Obtained With an Auto Transformer.
w
Fig. 242 — Another Method for "Obtaining Loose
Coupling With an Auto Transformer.
A popular opinion seems to exist that the required loose coupling for radiating a pure and
sharp wave can only be obtained by use of the inductively coupled oscillation transformer.
Contrary to this belief, however, a pure wave can be obtained by other methods of coupling
as well. Take, for example, the auto-transformer shown in Fig. 241. By the use of three
220
PRACTICAL WIRELESS TELEGRAPHY.
contact clips, the turns for the aerial circuit can be included between C and D and for the
primary circuit between A and B. With the taps in this position, the mutual inductance is
reduced and the coup-
ling
The
s s CAROUNA
Date 3:!P:M6 Tuned by' * B.COLLE50N ""
TUNING RECORD
Call Letters .....KGB.
• Type of Equipment ..:?.. ^ W. 500 ~ /R
Aerial Type T. No. of Wires—
_JT — Aerial Natural vA'
WAVE-LENGTH — 3OO —
450 — 600
Primary ' /A
L-A— ~-A Turns
Secondary
...4-^. .4. V|fe " Aerial Capacity
Loading Coil (Fixed) 8A
*[A.^ I? ^4 " M'f'ds
" (Var.^ 3_± _
...3± _3 ±_ '-
'Short Wave Condenser J-N.
PUT .PUT In or Qut Condenser
. ' jars
Radiation Quenched 5«Q
Decrement ... r.PrI??
p,)Q ,055 300 .._! _
"3
Radiation Rotary _- ?-P -
7.0 IO,Q Amperes 45° ~<
%
|
Decrement .. ..Or.'.?
0.10 ,055 _ too — fe —
~
Coupling ..? FOR WENCHED &
f PR. ROTARY..... _
Fig. 243 — Ship Tuning Record (American Marconi Company).
in accordance.
radiated wave
may therefore possess
a damping factor as
low as that obtained
with the inductively
coupled system.
If the coupling re-
quires still further re-
duction, contacts C
and D are moved up-
ward and away from
A, B, care being taken
to keep the same
number of turns be-
tween C and D in
order to maintain res-
onance.
Loose coupling can
be obtained as shown
in Fig. 242 where the
condenser C is of
such capacity that to obtain resonance with the antenna circuit only one-half turn is required
between A and B. Hence, the mutual inductance between the open and closed circuits is small
and the radiated waves approach unity.
183. Measurement of High Voltages. — The maximum voltage per alter-
nation of a high voltage current can be obtained by the sphere gap method.
Two brass spark balls, two centimeters in diameter, are mounted on an insulating
base and arranged so that the length of the gap can be increased or decreased by
a micrometer adjustment.
The gap is then connected to a given source of high voltage current and the gap length-
ened until sparking just ceases. For a given separation of the electrodes, the voltage corre-
sponding thereto is shown in the following table:
Spark Length in
Millimeters.
1
2
3
4
5
6
7
8
9
10
11
12
14
Voltage.
4,700
8,100
11,400
14,500
17,500
20,400
23,250
26,100
28,800
31,300
33,300
35,500
38,700
Spark Length in
Millimeters.
16
18
20
22
24
26
28
30
32
' 34
36
38
40
Voltage.
41,300
44,700
47,400
49,800
52,000
54,000
55,800
57,500
59,000
60,400
61,800
63,000
64,200
184. Tuning and Adjustment Record. — After a radio transmitter of any
type has been adjusted by a Marconi Inspector, a complete tuning record is posted
in the operating room. A typical record is shown in Fig. 243, which, as will be
observed, indicates the number of turns in the primary and secondary windings
of the oscillation transformer, also in the loading coils for each of the three
standard wave lengths. In the event of repairs being made, the adjustments
noted on this record must positively be duplicated.
PRACTICAL RADIO MEASUREMENTS.
221
In counting the helix turns for any standard wave, the operator should note
first, the point on the helix at which the circuit begins and also the general direc-
tion of the turns for an increase of inductance. Pie should then be sure to count
the number of complete turns of inductance and not merely the bonds on the helix.
TURNS
3 TURNS
COUPLING
| TURN COMMON
COUPLING: 8 INCHES
OR IF GRADUATED
SCALE GIVE READING^
THUS: COUPLING i
SCALE 14 '
Zj TURNS
COUNTING
FROM
OUTSIDE
2 TURNS -
COUNTING FROM
OUTSIDE
l{ TURNS
— G
TURNS
COUPLING 4
INCHES OR IF
GRADUATED SCALE
/'GIVE READING THUS!
COUPLING SCALF 14.5
TURNS
2{ TURNS
COUPLING
NO COMMON
TURNS
BETWEEN PAS
l{ TURNS
I TURNS
COUPLING 4 INCHES OR
IF GRADUATED SCALE, GIVE
READING THUS.
COUPLING SCALE 4.6
— G
TURNS
OR IF 6RADUMID COUPLING
SCALE IS PROVIDED. INDICATE
THUS COUPLING SCALE 45°
Fig. 244 — The Method of Checking up Coupling and Turns of a Helix as Authorized
by the U. S. Government.
The tuning adjustments of the quenched spark discharger are invariably rather critical
and, therefore, the settings of inductance noted on the tuning cards must be more closely
duplicated than for sets employing simple types of spark dischargers. A slight variation of the
antenna inductance is permissible from time to time to compensate for detuning occasioned
by sagging of the wires.
222
PRACTICAL WIRELESS TELEGRAPHY.
The coupling reference at the bottom of the card refers to the coupling of the primary
and secondary windings on the panel sets shown by the scale attached to the coupling
handle. The notation "8 for rotary" means that the coupling for the rotary gap is less than
for the quenched gap or at least the primary and secondary windings have greater separation
than for title quenched gap.
The notation condenser jars refers to the number of jars in use in the closed circuit.
MARCONI WIRELESS TELEGRAPH COMPANY- OF AMERICA
STATION /» £- / tH L>
SECONDARY SCALE SETTINGS.
Fig. .245— Curve Showing Reduction of Current by Turning the Secondary Winding of the Type A
Oscillation Transformer at Right Angles to the Primary Winding.
Diagrams showing the different ways Government Inspectors record the coupling and
the number of primary and secondary turns for the standard wave lengths are shown in
Fig. 244 which is a duplicate of the drawings printed on the rear of the Government tuning
record (form 766). Duplicates of these sketches are drawn in on the Government tuning
record by the Government Inspectors and the exact number of turns for the standard waves
in either circuit plainly marked for operator's reference. In certain standard types of
Marconi apparatus, a diagram showing the turns in use is not required; the inspector
merely marks the number of turns for the standard waves in both the primary and secondary
windings.
We have shown in paragraph 103 how the coupling of the type A oscillation transformer
is reduced by turning the secondary winding at an angle to the primary. It is also mentioned
in paragraph 202 that the antenna current can in this way be progressively increased from
zero to maximum.
In the curve shown in Fig. 245 the antenna current corresponding to various angles of the
secondary winding is plotted in the form of a curve. Such" records are posted in the
operating room. It will be observed in Fig. 245 that when the secondary winding bears an
angle of 90° to the primary winding, the antenna current is zero, but, as the secondary
winding is turned towards maximum coupling, the antenna current gradually increases to
8J/2 amperes. By giving careful attention to the data shown in Fig. 245 the operator is
enabled to communicate with ship or shore stations with the minimum of interference, using
such values of antenna current only as will enable the desired distance to be covered.
There is no hard and fast rule to lay down for determining the correct value of antenna
current for transmitting over a given distance, but after a few experimental trials with
various stations, the minimum current for a given range is easily found out.
PART XII.
STANDARD MARINE SETS OF THE AMER-
ICAN MARCONI COMPANY.
PANEL TRANSMITTERS— COMPOSITE TRANSMITTERS.
185. PANEL TRANSMITTERS. 186. DETAILS OF TYPE P-4
PANEL. 187. DESCRIPTION OF APPARATUS. 188. COMPLETE
ADJUSTMENT OF TYPE P-4 SET. 189. TYPE P-5 PANEL TRANS-
MITTER. 190. DESCRIPTION OF APPARATUS. 191. COMPLETE
ADJUSTMENT OF THE TYPE P-5 SET. 192. How TO REMOVE
THE ARMATURE OF THE l/2 K. W. MOTOR GENERATOR. 193.
THE 1 K. W. NON-SYNCHRONOUS DISCHARGER TRANSMITTER.
194. DESCRIPTION OF THE SET. 195. INSTALLATION. 196.
ADJUSTMENT OF THE 1 K. W. SET. 197. TYPE "E-2" ONE-
HALF KILOWATT, 120 CYCLE PANEL TRANSMITTER. 198.
DETAILS OF THE CIRCUITS AND APPARATUS, 199. GENERAL
INSTRUCTIONS FOR TUNING AND ADJUSTING. 200. MARCONI
2 K. W. 240 CYCLE TRANSMITTER. 201. TYPE P-9 y4 K. W.
CARGO TRANSMITTING SET. 202. AERIAL CURRENT AND REDUC-
TION OF POWER. 203. GENERAL INSTRUCTIONS FOR THE PANEL
SETS.
185. Panel Transmitters. — In point of efficiency, general utility, economy
of space, and ease of installation, the panel transmitter units of the Marconi
Company of America excel. Three types are now supplied for marine service
known as Type P-4, P-5 and P-9. The former has a normal power consumption
of 2 K. W.', the latter y2 K. W.
The 2 K. W. set has a daylight range of 450 to 650 miles, 1,500 to 2,500 miles
after dark. The */> K. W. set has a daylight range varying from 250 to 400
miles, 600 to 1,500 miles after dark.
Panel transmitter type P-4 is furnished for vessels of large tonnage requiring
the maximum possible transmitting range, but type P-5 is particularly suitable
for small yachts, cargo-carrying vessels and tug boats. It should be kept in mind,
however, that set P-5 has sufficient range to comply with the international regu-
lations on vessels of any tonnage.
Although the y2 K. W. and 2 K. W. panel transmitters arc now standard for ship service,
a number of vessels in the American Marconi Company's service are still fitted with com-
posite sets popularly known as the "1 K. W. non-synchronous set" and the "2 K. W. 240
cycle set.'' Several vessels are fitted witli a J/2 K. W. 120 cycle panel transmitter (Type E-2)
but the manufacture of this type has been discontinued.
Ill this chapter, all sets now in use in the ship service will be described in de-
tail and such information will be supplied as will enable the operator to adjust the
apparatus to its maximum degree of efficiency. The 2 K. W. panel set will first
be described*
STANDARD MARINE SETS OF AMERICAN MARCONI CO. 225
186. Details of Type P-4 Panel. — The complete 2 K. W. panel set comprises
the following apparatus:
(1) Panel Transmitter consisting of the necessary power measuring instru-
ments, oscillation transformer, condenser, variable and plug type aerial
tuning inductance, quenched spark gap, motor and generator field
rheostats, wave length changing switch, several resistance units and a
compensating reactance regulator.
(2) Crocker- Wheeler or General Electric 2 K. W. 500 Cycle Motor Generator
with synchronous rotary spark gap mounted on the generator shaft, pro-
tective condensers, starting resistance, automatic motor starter and neces-
sary controlling appliances.
(3) Type 106 Receiving Tuner with crystal rectifier and head telephone
receiver.
(4) Type I Aerial Change-Over Switch with necessary appliances for protect-
ing the receiving apparatus from the transmitter.
(5) Type C Transmitting Key.
(6) High Potential Closed Core Transformer.
In addition to the foregoing apparatus, the owners of the vessel supply a 60 cell storage
battery and a charging panel fitted with the necessary appliances- for controlling the charging
circuits. With an aerial equipment like that described in paragraph 117, the foregoing ap-
paratus completes a standard marine wireless telegraph equipment.
A simple fundamental diagram of the complete circuits of the type P-4 transmitter
and receiver is shown in Fig. 246, a front view of the panel in Fig. 247, a side view in Fig.
248 and a rear view in Fig. 249.
187. Description of Apparatus. — The motor generator consists of a 4 H. P.
110 volt 2 pole direct current motor connected directly to a. 2 K. W. 500 cycle alternator.
The motor is specially constructed to operate with little variation of speed on pressures
varying from 95 to 115 volts.
The generator is of the rotating armature type, having a normal open circuit voltage of
350 volts, and a working or load voltage of 140 volts. The voltage of the generator is varied
by a rheostat of the sliding contact type mounted on the right hand side of the panel, and
the speed of the motor by a similar rheostat on the left hand side of the panel. (See
Fig- 247.) | !*«
An automatic motor starter is provided which permits the motor to be controlled from a
distant point in the operating room. The starter is of the magnetic plunger type having a
piston which travels through a cylinder compressing the air on one side and cre-
ating a vacuum on the other. The speed of the armature accelerates uniformly and the
time of completing the circuit may be varied by a special adjustment screw attached to the
starter.
The starter is fitted with an clcctrodynamic brake which comprises a resistance coil
thrown in shunt to the armature when the current to the motor is turned off. By means
of this brake, the motor is brought to a standstill within ten seconds.
An overload relay switch connected in series with the armature automatically opens the
D. C. circuit to the starter solenoid when current in excess of a certain number of amperes
passes through the motor windings. In case of overload, the plunger of the starter drops
down breaking the main circuit to the motor armature. The circuit of the solenoid then
remains open until the main D. C. line switch is opened by hand. If a short circuit exists
in any part of the wiring and the power switch is closed again, the relay will open the
circuit once more and continue to do so until the trouble is located. The relay is generally
adjusted to open at 35 amperes.
Each terminal post of the motor generator is connected to one terminal of a protective
condenser to neutralize differences of potential that may be set up by electrostatic induction
from the transmitting apparatus. The opposite terminal of the condenser is connected to
the frame of the motor generator and then to earth (see Fig. 79). Six protective condensers
are provided for each motor generator, and enclosed in a metallic case. The frame of the
motor generator and also the lead covered wires connecting to the apparatus on the panel
are thoroughly connected to earth.
226
PRACTICAL WIRELESS TELEGRAPHY.
AERIAL
AMMETER
MOTOR
RHEOSTAT
COUPLING
ADJUSTED
WATTMETER
GENERATOR
.-RHE05TAT
AERIAL TUNING
~~ INDUCTANCE
-WAVE LENGTH
CHANGING SWITCH
MOTOR
GENERATOR
QUENCHED
i-— GAP
OVERLOAD
RELAY
AUTOMATIC
"STARTER "oe"'
ROTARY
GAP
Fig. 247— Front View Marconi 2 K. W. 500 Cycle Transmitting Set.
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
-SLIDING CONTACT
CONTINOUSLY VARIABLE
TUNING INDUCTANCE
PLUG AER\AL TUNING
!NDUCTA!^4CE
227
SECONDARY
/OSCILLATION
TRANSFORMER
PRIM.WAVE LENGTH SWITCH
SPARK GAP CHANGING SWITCH
STATIONARY ELECTRODES
ROTARY GAP
WAVE. LENGTH
SECONDARY SWITCH
MOTOR
'STARTER
RESISTANCE
STEP UP TRANSFORMER
Fig. 248— Side View Marconi 2 K. W. 500 Cycle Transmitting Set.
228
PRACTICAL WIRELESS • TELEGRAPHY.
AERIAL TUNING INDUCTANCE
SEC. WAVE LEN&TH
CHANGING SWITCH
The circuit from the alternator to the transformer includes a direct reading wattmeter
for indicating the power consumed by the transformer. The current coil of this instrument
is connected in series with the transformer primary and the potential coil is connected across
its terminals.
The high voltage transformer, of the closed core type, is immersed in a semi-liquid
grease. The primary wind-
ing is connected to the con-
trol panel by means of lead-
covered wires which have
their covering grounded to
the transformer case and to
the panel frame. The sec-
ondary terminals of the
transformer are brought out
through two insulators and
are mounted thereon. A
protective spark gap is pro-
vided which permits a dis-
charge in case the voltage
exceeds a certain critical
value. The secondary po-
tential is approximately 12,-
500 volts. The secondary
terminals of the transformer
are connected directly to the
terminals of the high poten-
tial condenser of the closed
oscillation circuit. Gener-
ally, the transformer is
screwed to the floor imme-
diately to the rear of the
control panel.
The transmitting con-
denser comprises six copper-
plated glass jars of .002
microfarads capacity each,
three of which are connect-
ed in parallel for the 300
meter wave, and six in
parallel for the 450 and 600
meter wave. These are
mounted in a metal rack,
placed directly underneath
the oscillation transformer
and connected thereto with
a multipoint switch to be
explained later.
MOTOR GENERATOR
MOTOR STARTER
RESISTANCE
ROTARY
SPARK GAP \1
TRANSFORMER
Fig. 249— Rear View Marconi 2 K. W. 500 Cycle Transmitting Set.
The oscillation trans-
former is of the inductively
coupled type, the primary and secondary windings consisting of a strip-copper, spiral wound
edgewise on a rectangular insulating support. The secondary turns for the three standard
waves are selected by means of three flexible plug connections, but the three taps on the
primary inductance for the 300, 450 and 600 meter waves are soldered fast in position,
connections being shifted from one wave to the other by means of a multipoint wave-length
changing switch.
Two aerial tuning inductances are provided, one being a continuously variable inductance
having a sliding contact which can be revolved by a handle in the front of the panel, per-
mitting the inductance to be increased or decreased inch by inch. The second aerial tuning
inductance, connected in series with this one, is fitted with three plug connections which are
placed at positions on the coils corresponding to the 300, 450 and 600 meter waves.
The short wave condenser, which consists of 2, 3 or 4 copper-plated jars connected in
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
229
series, mounted in a metallic rack, is shown connected in the aerial circuit in Fig. 246. When
not in use, the jars are shunted by a flexible conductor or by a switch.
The aerial ammeter is a direct current instrument, range 0-20 amperes, its terminals being
connected to a thermo-couple which is in turn mounted on a heating wire, the latter being
connected directly in series with the antenna system. (See Fig. 53.)
The Type I Aerial Change-Over Switch is
fitted with the necessary contacts for opening
and closing the transformer primary circuit
and for protecting the receiving tuner circuits
during the periods of transmission. It also discon-
nects the secondary winding of the oscillating trans-
former from the transmitter aerial during the re-
ceiving period, interrupts the field circuit to the gen-
erator, and starts and stops the motor generator.
This switch is described in detail in paragraph 155.
The predominant feature of the 2 K. W. 500 cycle
set is the specially designed wave-length changing
switch, the function of which will be fully described
in paragraph 188, section d. This switch auto-
matically shifts the coupling, inductance and capacity
values for the three standard waves, the entire opera-
tion being performed by merely throwing a handle
mounted on the front of a panel.
To meet the government requirements, provision
is made for transmitting at low power. A fixed re-
sistance connected in series with the generator field
permits the voltage of the generator to be reduced to
the lowest operative condition. The switch marked
"low power" shunts this resistance coil, and, when
open, only one or two gaps of the quenched dis-
charger are to be employed.
Type P-4 set is equipped with a synchronous
rotary gap, having 30 sparking points, mounted on the
shaft of the motor generator, the disc being thor-
oughly connected to earth ; also a quenched spark gap
consisting of 15 plates mounted in a metal rack and
insulated therefrom. The disc of the rotary gap is
fitted with air circulating vanes which force air at
uniform pressure through a specially designed air
duct to the plates of the quenched gap.
188. Complete Adjustment of Type P-4 Set.— (a) Plunger Control Auto-
matic Starter. The plunger of the automatic motor starter should be adjusted to reach the full
running position within 12 seconds. A small regulating screw P, Fig. 251, is placed directly
underneath the plunger chamber and, if turned to the right, the plunger moves up slowly,
but to the left, rapidly. The contacts F, G, H, I, J, which make connection with the crossbar
on the plunger K, should be adjusted to complete the circuit to the armature in progression;
e. g., one is placed a little bit higher than the other as shown.
Set screw U should be adjusted until lever O of the overload relay is opposite 30 or 35
amperes. This is approximately the correct setting for average working. The tension on the
springs attached to the upper contacts of the automatic starter, should be adjusted for firm
contact with bar K.
The circuit to the solenoid N is opened and closed at T-l while contact T closes the cir-
cuit to a special magnet winding holding lever O upward in case of short circuit in the
power circuits. Contacts Y and Z throw a small resistance coil in series with the solenoid
winding after the starter has reached the full running position. A simple fundamental
wiring diagram of this starter appears in Fig. 75.
(fc) Adjustment of the Spark Note. In the adjustment of the note of the quenched spark
discharger, it is to be understood that the pitch depends upon conditions of resonance
between the open and closed oscillation circuits as well as upon the voltage of the generator.
Careful regulation of the voltage, however, is the principal adjustment and the one to be
undertaken first (provided the set has been tuned).
Type
Panel Transmitter (American Mar-
coni Company).
230
PRACTICAL WIRELESS TELEGRAPHY.
The operator should select a certain number of gaps, say eight, and follow it by varying
the generator voltage. After the set has been tuned for maximum antenna current, the
voltage should be slightly readjusted until the spark is clear.
It is easily seen that if the note is clear and the secondary circuit is thrown out of
resonance, less energy will 'be withdrawn from the closed oscillation circuit, which will
increase the voltage across the gap. The pitch of the note will therefore be destroyed.
The rule to be followed is, tune the set first; afterwards adjust the gaps and voltage until
the note is clear and the wattmeter indkates 2 kilowatts.
The synchronous rotary gap is adjusted for a high pitched note by the small brass rod
R and knob, Fig. 116, which moves the muffling drum carrying the stationary spark elec-
trodes through a 25-degree arc.
It is also essential that the A. C. voltage be carefully regulated. But the operator should
take care that the reading of the wattmeter in no case exceeds 2 K. W. Also he should
adjust the length of the discharge gap until the stationary electrodes and the rotary elec-
trodes are separated no more than .01 of an inch. The complete process will perhaps be
clearer from the detailed drawing, Fig. 252.
OVERLOAD REUW
o o o o
o
P-6
O
P6
O
PIO
o
p-ll
o
P12
o
PIS
o
PI4
O
P-15
Fig. 251 — Automatic Starter Panel (2 K. W. 500 Cycle Transmitter).
It is important that this adjustment be not undertaken until the motor is stopped. Then
one stationary electrode is lowered down by means of the milled screw S until it touches one
of the electrodes on the disc. The electrode is then raised to just miss the rotating electrodes
vvhen the disc is turned over by hand. Similarly the other stationary electrode must be
lowered until it touches the disc electrodes and then raised until it clears the entire set of
spark points on the disc.
Each turn of the nut S represents a radical movement of .037 of an inch and as there are
eight holes equally spaced in the face of the nut (which engage the pin P), the movement
of one hole represents a radial movement of approximately .005 of an inch. The length of
the spark discharge gap is adjusted correctly when the electrodes on the disc and the sta-
tionary electrodes are separated .005 of an inch to .01 of an inch, and, after they have been
so adjusted, the muffling drum should be shifted backward or forward until a uniform
clear spark note is obtained.
(c) Details of Quenched Gap. A detailed front view of this spark gap partly in section
is shown in Fig. 253. The quenched gap consists of a number of copper discs or plates such
as O, O, having circular sparking surfaces J separated by paper washers which are specially
treated with an insulating varnish. These plates are set in a trough and clamped together
with such pressure that the space enclosed between the discs is airtight. A disc or insulating
material F is placed against the end plates to insulate the gap from brackets K and C. Con-
tacts P and Q, which extend to the condenser and oscillation transformer, may be plugged
into the cooling flanges of any of the plates. Nuts D, D brace the end castings K and C.
Operators of the Marconi service should give the following instructions careful consider-
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
231
INSULATING
/BUSHING
ation : In setting up the quenched gap care should be taken to keep the spark surfaces J
absolutely clean and smooth. The paper discs or washers N should also be scrupulously
clean. Fifteen plates are stacked up in the rack and pressure applied through the pressure
_ bolt B, which is locked in position by the
nut A. This screw should be taken up with
a 10-inch monkey wrench.
If the gap is not airtight the spark note
will be irregular. This is a positive indica-
tion that the gap is leaking and it should
therefore be taken apart and the sparking
surfaces cleaned and reassembled, using new
gaskets if necessary. The gap should not be
used over an extended period if it once starts
leaking.
In case one of the gaps become defective
it can be short-circuited by means of a metal
contactor which is furnished especially for
that purpose. The defective gap can be de-
tected by means of a short circuiting contact
mounted on an insulating rod called a test
rod. The gaps can be successively short-
circuited and the defective one will be located
by there being no sparking at the tips of the
contactor.
In event the gap is . taken apart, before
being reassembled, the sparking surfaces of
the copper plates must be cleaned and
smoothed off by means of very fine sand-
paper. Care should be taken to keep the sur-
faces perfectly flat during the cleaning so
that the opposing surfaces will be parallel
when they are placed in the rack. When the
gap is in proper working condition, the
sparking surfaces show a uniform coloring
over the whole area. // the surfaces of the
plate are black or dark colored, it is an indi-
cation that the gap is not airtight.
If it becomes necessary to disassemble the
gap, after reassembly, the spark must be dis-
charged through the series of plates con-
tinually for one or two hours. In fact, the
note will not be clear until the gap is thus
"seasoned."
(d) Tuning and Wave-Length
Changing Switch. It has long been the
desire of radio engineers to fit the trans-
Fig- 252™Showi"! HT the st*tionary S^ctr,°3es of mitting apparatus with appliances
the Marconi Synchronous Gap are Adjusted. 111 1 i r i
whereby the wave-length of the trans-
mitting set could be quickly changed by merely throwing a switch, but the re-
quirements of radio-frequency circuits would not permit this to be done without
certain mechanical and electrical considerations.
For example : With the potentials employed in radio-telegraph transmitters, the switch
to perform these functions must possess first-rate insulating qualities. The associated circuits
and leads thereto must be widely separated and in addition they must not be of too great
length in order that the length of the radiated wave may be kept within restrictions. Again
the component parts of the complete switch cannot be placed in any convenient mechanical
position but must perform their functions near to the portion of the circuit in conjunction
with which they operate. Additional considerations are involved obvious to the radio
engineer, but not of sufficient importance to be gone over in detail.
The complete process of tuning of the 2 K. W. 500 cycle sot, and the locating of the taps
STATIONARY
ELECTRODE
ELECTRODE
OH DISC
232
PRACTICAL WIRELESS TELEGRAPHY.
on the secondary turns of the oscillation transformer may appear difficult to the unskilled
operator, but is easily accomplished by the trained engineer or inspector.
The function of the wave length changing switch and the tuning of the 2 K. W. 500 cycle
get will be described in detail and reference should be made particularly to Fig. 246 showing
the complete circuits of the apparatus.
First it should be noted that when the quenched spark discharger is cut in the circuit, the
coupling betiveen the primary and secondary windings is varied by varying the number of
turns in the secondary winding only, the primary and secondary coils being placed in a
fixed mechanical position, but for the synchronous rotary spark gap they are drazvn apart to
whatever degree of separation is necessary to radiate a pure wave. In certain installations
the primary and secondary windings may be placed in a fixed mechanical position for the
rotary discharger as well as for the quenched gap.
(1) Explanation of the circuits. It will be. observed from the diagram, Fig. 246, that
these sets are fitted with a change-over switch which permits either the rotary disc discharger
or the quenched spark discharger to be cut in the circuit. The gaps are connected in series
and to change from one to the other, it is only necessary to shift the position of the switch
K. When the quenched discharger is in use, a compensating inductance L, Fig. 246, makes
up for the length of leads connected from contacts 58 and 59 to the rotary disc discharger,
thereby keeping the wave-length of the closed oscillatory circuit constant. When the rotary
D _*s
Fig. 253— Detailed Sketch of Marconi Quenched Spark Gap.
discharger is connected in the circuit, the flexible leads attached to the quenched gap plates
must be connected together.
In the diagram, Fig. 246, the high potential transformer of the set is represented by the
primary and secondary windings P and S respectively; the high potential condensers at C-l
and C-2; the primary winding of the oscillation transformer at P-l, the secondary at S-l ;
also an aerial tuning inductance S-2 with flexible contacts A, B and C, and, in addition, a
continuously variable tuning inductance S-3. The antenna system further includes the series
condenser C-3 and the aerial ammeter. The distinctive feature of this apparatus is the
primary wave-length changing switch W-l operated simultaneously by a single handle in
conjunction with the switch W-2. It will be observed that when W-l is in contact with
point 39, a single unit of the condenser C-2 (three jars in parallel of 0.002 microfarads each)
is connected in series with the primary winding of the oscillation transformer at point A,
i.e., the adjustment for 300 meters.
Similarly, W-2 closes the aerial circuit to contacts 44 and 45, which connect in the correct
number of turns to radiate the 300 meter wave. Contacts A, B and C of S-l and S-2 may
be plugged in at any point on the secondary coil, but they are permanently attached to the
coil after the set has been tuned to the three standard waves. Further movement of the
handle connects together contacts 40 and 41, which not only connects in the correct number
of primary turns for the wave-length of 450 meters, but also connects the condenser units
C-l and C-2 in parallel, giving a total condenser capacity of 0.012 microfarads. Still further
movement of the switch closes contacts 42 and 43, also contacts 48 and 49, which connect in
STANDARD MARINE SETS OF AMERICAN MARCONI CO. 233
the correct number of turns, in both the open and closed oscillatory circuits, for the standard
600-meter wave.
(2) The Process of Tuning. Before undertaking to tune a set of this type, the student
should thoroughly consider the following facts:
(1) In order to obtain the maximum flow of antenna current, a different
degree of coupling at the oscillation transformer must be found for each
of the standard waves.
(2) In order that the radiated waves can be rapidly changed by simply throw-
ing a switch, the primary and secondary windings of the oscillation trans-
former must remain in a fixed position mechanically.
(3) The coupling of the oscillation transformer is then varied for each
standard wave by changing the self-inductance of the secondary, i. e.
cutting in or out turns.
Now the correct number of turns for the secondary winding is determined for each of
the standard waves experimentally, as follows :
For preliminary determination at a standard wave-length, say 600 meters, a trial number
of turns (4 to 6 turns) is selected at the secondary winding S-l through the flexible plug
contact C. This having been done, a second trial number of turns, say 4 turns, are cut in
at S-2. Turns are added or subtracted at the aerial tuning coil S-3 (with the spark gap
discharging) until the aerial ammeter indicates a maximum deflection. The adjustment
for resonance having thus been located, the windings P-l and S-l are drawn apart or placed
closer to ascertain if an increase of antenna current will result. If separation of P-l and
S-l increases the antenna current, it indicates that too many turns have been included at S-l
for the mechanical position of the coupling coils selected at the start; and, in consequence,
turns must be taken out at S-l and additional turns cut in at S-2 or S-3, until resonance is
secured. The primary winding P-l must, however, first be placed in its original fixed posi-
tion relative to S-l. The correct number of turns must now be found out for the standard
waves of 450 and 300 meters, that is, the correct number of turns must be selected and the
coupling adjusted until the maximum antenna current for each wave is secured with P-l
remaining in a certain fixed position to S-l. At first sight, it may seem difficult to locate
the correct position for contacts, A, B and C, on S-l and S-2, but from the experience
obtained by tuning several sets, approximately correct inductance values may be selected at
sight. It should be understood that the positions of A, B and C on the primary and
secondary coils shown in Fig. 246 do not necessarily represent their relative positions in
actual commercial practice. With aerials of different capacity, inductance, and resistance,
decidedly different positions must be located. For example: At the wave-lengths of 450
and 600 meters, less inductance may be required at point C than at point B for these two
wave-lengths, or vice versa.
Careful consideration of the foregoing procedure will reveal that (1) the continuously
variable inductance S-3 aids in locating the number of turns to be finally connected in at
S-2; (2) S-3 gives a fineness and quickness of adjustment which the coil S-2 with a flexible
contact does not afford; (3) the mechanical variation of the coupling between P-l and S-l
permits the correct number of turns to be selected much more quickly than by experimental
trials with the plug contacts.
It is now clear that after the set has been completely tuned, in order to change from one
standard wave-length to the other, the operator needs only to shift the handle of the switches
W-\ and W-2, with the exception that on the 300-meter wave, the short wave condenser C-3
must be connected in series with the aerial system. In certain ship installations, the eon-
denser C-3 is connected in series with the lead from contact 45 to the aerial tuning induct-
ance S-2 and when so connected is automatically thrown in series with the antenna system
whenever the switch blades W-l and W-2 are shifted to the 300-meter position.
Because of the perfect quenching secured with this particular type of gap P-l may remain
in a fixed mechanical position relative to S-l throughout the series of wave-lengths, but
when the rotary disc discharger is employed, unless a complete new set of positions is
located for contacts A, B and C of S-l and S-2, P-l must be drawn away from S-l to
secure a pure wave. P-l might have to be placed from eight to ten inches away from S-l
to radiate a pure wave with the rotary gap.
The primary and secondary wave-length changing switch performs another function
which has not been mentioned : When the switch is in the 300-meter position, a reactance
foil is automatically connected in series with the primary winding of the power transformer
234
PRACTICAL WIRELESS TELEGRAPHY.
TERMINAL
to reduce the power to a value commensurate with the decreased secondary condenser capacity.
The transformer then consumes 1 k. w.
During the tuning of these sets it has been observed that if initial adjustments are made
near to metallic dock buildings, the effective antenna resistance is altered, and, in conse-
quence, the tuning adjustments for maximum antenna current, need to be changed slightly
zvhen the ship is at sea. Generally it is only necessary to vary slightly the inductance of S-3
for maximum aerial current.
After the set has been tuned in this manner, the purity of the wave and decrement of
the oscillations is measured by means of a wavemeter with a current indicating instrument
connected in series, such as a wattmeter.
The commercial value of a transmitting set equipped with these features cannot be over-
estimated. The operator having at his disposal three standard wave-lengths, any of which
may be brought instantly into play, can
literally pick his way through the con-
gested radio atmosphere, changing from
one wave-length to the other as operating
conditions may require.
O) Type 106 Tuner. The working and
adjustment of this tuner is completely cov-
ered in paragraph 138 of Part IX.
(/) Short Wave Condenser. This con-
denser consists of 2, 3 or 4 jars connected
in series. Owing to the variation in the
capacity of commercial aerials, the correct
capacity for the short wave condenser is
best determined by experiment. Two
standard jars in series have capacity of
.001 mfds.; three in series .00066 mfds., 4
in series .0005 mfds. Aerials having a
natural wave-length of 250 meters do not
require a short wave condenser for three
JAR
254— One
Type of Marconi
Condenser.
Short Wave
standard waves. A side view of one type
of short wave condenser is shown in
Fig. 254.
(g) Spark Gap Change-Over Switch.
To change from the quenched to the
rotary gap, a small D. P. D. T. switch is
connected in the circuits of radio-fre-
quency. When the rotary gap is connected
in the circuit, the quenched gap is placed
on short-circuit by connecting together the
contact clips.
189. Type P-5 Panel Transmitter. — In many respects this set duplicates
the type P-4, but there are certain mechanical modifications. The motor gen-
erator and the transformer are mounted on the panel frame together with the
remainder of the equipment. Both the rotary synchronous discharger and the
quenched discharger are supplied. A compensating inductance joined to the
change-over switch permits the use of either spark discharger without change
of the wave-length of the closed oscillation circuit.
A fundamental circuit diagram of the automatic starter for this set has been shown in
Fig. 74 and a more detailed diagram is now presented in Fig. 255. The circuits of radio-
frequency are shown in Fig. 256; a front and side view of the panel in Fig. 257 and Fig.
258 and a rear view in Fig. 259.
190. Description of Apparatus. — The motor generator comprises a 110 volt
direct current motor directly connected to a y2 K. W. 120 volt 500 cycle alternator.
The motor is designed to operate on pressures between 95 and 115 volts with little change
of speed. The initial speed is controlled by a rheostat mounted on the left hand side of
the panel.
The generator is of the inductor type having a stationary armature and field winding, the
flux being varied by a rotor of soft iron. (See photo, Fig. 67.) The open circuit voltage
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
D.C. LINE
235
D.C. FIELD
RHEOSTAT
AUTOMATIC STARTER,
l.C.Co. D.C. i K.W. 110
VOLT, TYPE T" WITH
DYNAMIC BRAKE.
Fig. 255 — Fundamental Wiring Diagram of the Automatic Starter Furnished With the Marconi
500 Cycle Transmitter.
K. W.
of the generator is approximately 350 volts and the load voltage about 120 volts. The
normal speed of the machine is 2,500 R. P. M. The voltage at the armature terminals can
be varied by the field rheostat mounted on the right hand side of the panel. The low power
circuits are protected by the usual set of protective condensers.
A closed core transformer having a secondary potential of 14,500 volts is supplied and is
fitted with an appropriate safety gap.
236
PRACTICAL WIRELESS TELEGRAPHY.
QUENCHED
GAP
GROUND CONNECTION
HELD IN PLACE
UNDER FLANGE NUT _^
Fig. 256— Radio Frequency Circuits of the ^ K. W. 500 Cycle Transmitter.
The circuits of radio-frequency (Fig. 256) are similar to the 2 K. W. set with the excep-
tion that a condenser of fixed capacity is employed throughout all wave lengths. Also the
secondary winding is moved away from the primary for change of coupling, which is the
reverse of the method employed in the 2 K. W. set. However, the change of wave-length is
accomplished in the same manner by a special switch and the primary and secondary wind-
ings remain in a fixed mechanical position for all wave-lengths.
The transmitter condenser consists of 4 copper-plated small Leyden jars connected in
parallel having capacity of .001 mfds. each. These are mounted in a metal rack behind the
panel.
This set is also fitted with a single pole double throw high potential switch which either
connects the aerial to the transmitter or connects it directly to earth for protection against
lightning. This switch operates independently of the antenna changeover switch.
The automatic starter supplied with this set has been shown diagrammatically in Fig. 74,
but the diagram, Fig. 255, outlines the circuits more as they appear on the actual panel.
The starter consists essentially of two magnets fitted with armatures, one of which con-
nects the motor armature to the D. C. line through a single resistance coil and the other cuts
out this resistance thereby connecting the motor direct to the D. C. line. Appropriate resist-
ance coils are connected in series with the solenoid windings automatically, when the starter
MOTOR
RHEOSTAT
AERIAL TUNING
INDUCTANCE "
WAVE LENGTH
SWITCH — f
AUTOMATIC'
-20|
WATTMETER
D C
A.C
GENERATOR
RHEOSTAT
AERIAL
AMMETER
LIGHTNING
" SWITCH
COUPLING
ADJUSTER
QUENCHED
GAP
ROTARY
GAP
Fig. 257— Front View of the Marconi y2 K. W. 500 Cycle Transmitter.
238
PRACTICAL WIRELESS TELEGRAPHY.
16"
TUNING
WAVE LENGTH x
CHANGING SWITCH
PRIMARY SECONDARY
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
239
CONDENSIR
is in the full running position. This
prevents the magnet windings over-
heating as the potential difference
across the motor armature rises. A
dynamic brake attached to the motor
starter consists of a shunt armature
resistance, which is connected across
its terminals by a special set of con-
tacts attached to the starter.
A 2-pole single-throw switch dis-
connects the motor from the power
line. A single-pole switch permits the
circuit of the generator field to be
interrupted as a matter of safety dur-
ing adjustment of the set and a sec-
ond D. P. S. T. switch breaks the
circuit from the generator to the
transformer.
The remainder of the equipment
consists of a Type I aerial switch.
Type 106 receiving tuner and flush
sivitch for starting and stopping the
motor generator from a distant point.
Also an aerial ammeter, range 0-10
amperes, and a direct reading watt-
meter, 0-750 watts.
191. Complete Adjustment
of the Type P-5 Set— (a) Tun-
ing. The tuning of this set, the ad-
justment of the frequency and the
voltage of the alternator and the ad-
justment of the rotary gap is prac-
tically the same as the 2 k. w. 500
cycle set described in previous para-
graphs. The adjustment of the
quenched gap is identical with the
method described for the 2 k. w. set
in section b, paragraph 188.
(6) Motor Starter. The opera-
tion of the y* k. w. starter shown in
Fig. 260 is as follows : The cut-out
switches of the automatic starter are
energized by direct current from the main D. C. line and operated by a distant control switch.
When this switch is closed, the solenoid "A" is energized and moves the contact arm C
radially in a vertical plane, perpendicular to the board, which cuts in the single resistance
unit mounted in the re-
sistance box behind the
panel.
As the speed of the
motor generator in-
creases, the current
falls off, and the poten-
tial difference across
the armature rises.
When it reaches normal
value, the solenoid B is
energized and draws
the contact arm F, cut-
ting out the resistance.
This connects full line
voltage across the
motor.
Fig. 259— Rear Vie\
j of the Marconi '
Panel Transmitter.
K. W. 500 Cycle
D.C.UNE
AC GEN
P< Ps P& PT
©000
Fig. 260— Automatic Starter Panel
K. W. 500 Cycle Transmitter).
240
PRACTICAL WIRELESS TELEGRAPHY.
CUT OUT FOR SHORT
WAVE CONDEN5ER
LOADING COIL
MOTOR FIELD GENERATOR
RHEOSTAT FIELD
RHEOSTAT
ABC ARE N° 5 MOUNTED
INSULATORS. D 15 PLUG
THIS IS TO CHANGE OVER
FROM COIL TO POWER AND
VICE VERSA
IZ CELLS
STORAGE BATTERY
Fig. 261 — Complete Wiring Diagram of Marconi 1 K. W. 60 Cycle Non-synchronous Transmitter.
The time of closing the contacts of the automatic starter is regulated by the set screw E,
Fig. 260, attached to the bottom of the starter arm B. Both solenoids should perform their
functions within six seconds from the time the starting switch is closed. Like in the 2 k. w.
set, the motor starter is controlled by a -special set of contacts mounted on the aerial change-
over switch or the motor may be held in a continuous state of operation by closing the flush
switch mounted near to the antenna switch. In the later models of this set, when the
starter is in full running position, resistances are cut in automatically at G and H to prevent
the solenoid windings overheating.
192. How to Remove the Armature of the y2 K. W. Motor Generator. —
To remove the armature for purpose of repair or replacement, it is necessary first to remove
the casing of the spark gap, then remove the disc, after which the bearing bracket can be
removed from the generator. Next remove the motor brushes after which the armature
can be pulled out. When replacing the armature the oil rings should be held up to permit
the shaft to pass through the bearings. The oil rings should then be placed in their slots
making sure that they move freely.
To remove the disc of the rotary gap, the small machine screw in the shaft key should be
unscrewed until it turns freely. A slight tap at the hub will then loosen the key which may
be removed by a pair of pliers. After this a slight tap on the hub of the disc will loosen the
other half of the key which may then be removed. The disc should then slip off readily.
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
241
193. The 1 K. W. Non-Synchronous Discharger Transmitter. Certain
ships in the Marconi service are fitted with a type of transmitter which originally was
designed to be operated from a 60 cycle motor generator, with a plain spark gap, but the set
is now fitted with a non-synchronous rotary discharger by which the effectiveness and range
has been materially increased. A complete circuit diagram of this set is shown in Fig. 261
and the lay-out of the transmitter and receiver in a silence cabin in Fig. 262.
194. Description of the Set. — The motor generator for this set is the
"Standard" Robbins and Meyers type. The motor is shunt wound for 110 volt direct current.
The generator is of 1 K. W. capacity and has an accumulative compound field winding
which tends to maintain a constant A. C. voltage under variable load. The generator delivers
current at 110 volts, 60 cycles. (See Fig. 65; also Fig. 79a.)
The circuit to the transformer is interrupted by a type C standard transmitting key.
The power transformer is of the open core type and is designed to operate on 110 volt 60
cycle circuits without external reactance. The secondary voltage is approximately 18,000
volts.
^STARTER
-MAIN LINE SWITCH
Fig. 262 The Installation of a 1 K. W. Transmitter in a Silence Cabin.
A hand-operated motor starter and two rotary field rheostats are supplied. The latter are
the Cutler-Hammer type.
The high potential condenser comprises 6 copper-plated jars of .002 mfds. each, con-
nected in parallel, mounted in a metal rack and insulated from the operating table by corru-
gated porcelain insulators. Connection between the outside coatings is established through the
frame of the rack. Only four jars are required, the remaining two being used as spares.
The oscillation transformer has been illustrated in Fig. 119. The primary winding is
made of copper tubing mounted on porcelain insulating supports. Tappings may be taken
from the primary inductance by means of special spring contact clips. The secondary wind-
ing has a fixed number of turns wound about an insulating drum which slides vertically on
a brass tube. One terminal of this winding is connected to the tube and the opposite terminal
to a terminal of the aerial tuning inductance.
The aerial tuning inductance consists of a number of turns of copper cable wound on and
insulated from a wooden frame. The required number of turns for any particular wave-
length are cut in by means of a contact clip attached to a flexible lead.
The short wave condenser consists of four copper-plated jars mounted on a rack insulated
242
PRACTICAL WIRELESS TELEGRAPHY.
STANDARD MARINE SETS OF AMERICAN MARCONI CO. 243
by corrugated porcelain insulators. Each jar has capacity of .002 mfds., consequently the
four in series have capacity of .0005 mfds.
The remainder of the equipment consists of a Type 106 Tuner, head telephone, Type I
aerial change-over switch, and the necessary aerial equipment.
195. Installation. — The component parts of the closed oscillation circuit
being mounted separately, short connecting leads must be employed to connect up the con-
denser, oscillation transformer and spark gap. Otherwise, it will be difficult to secure the
wave-length of 300 meters. Perhaps the best arrangement of the apparatus is that shown in
Fig. 262, where the transmitting apparatus is installed in a silence cabin, the operating room
having the receiving tuner, the motor starter, rheostats, the transmitting key and the aerial
change-over switch.
In the transmitting cabin, the rotary gap is mounted atop the high potential transformer ;
the oscillation transformer and condenser on the table immediately above.
The motor starter should be installed where it is convenient to the left hand of the
operator.
Lead-covered cable is used to connect up the power circuits, No. 10 S. B. R. C. being
used for the circuits carrying heavy current, and No. 14 S. B. R. C. for the field circuits and
rotary-gap motor. Copper tubing is generally used for the radio-frequent circuits and copper
ribbon for the earth wire. The receiving tuner is connected to the aerial switch by No. 18
fixture wire.
196. Adjustment of the 1 K. W. Set. — (a) Regulation of Voltage and Fre-
quency. Care should be exercised not to overload this set by the use of abnormal voltages
at the generator. These machines are constructed so that when 110 volts D. C. is supplied
to the motor 110 volts A. C. is supplied by the generator. The contact on the generator field
rheostat should occupy an approximate midway position for the correct voltage while the
motor rheostat should be set at the zero position; e. g., all resistance cut out of the circuit
(when the voltage of the ship's generator is normal).
(&) Rotary Gap. The arm of the rotary gap should be driven at approximately 2,400
R. P. M., but should be regulated according to the pitch of the note; in other words, the
speed giving the clearest note is the one to use. A small speed controlling rheostat is
mounted in the instrument room convenient to the operator. The adjuster should work
in the direction of obtaining a note of high pitch with low values of voltage at the generator
rather than with excessively high voltages. The gap between the points of the rotor and
those on the stationary arm should be adjusted to a minimum length.
(c} Tuning. The tuning of this set is accomplished by first tuning the closed circuit to
one of the standard waves with a wavemeter, followed by a similar adjustment of the aerial
circuit. The better method is to excite the antenna with a spark coil or vibrating buzzer
and in this manner measure the natural wave length of the aerial, then add turns at the
aerial tuning inductance until the wave-length of 600 meters is obtained. Proceed similarly
for 300 meters, but the short wave condenser must be connected in series with the aerial
and perhaps another selection of turns made at the aerial tuning inductance.
The degree of coupling and the consequent purity of the radiated wave may be adjusted
by raising or lowering the secondary winding in respect to the primary winding, on the
vertical rod or post. The secondary winding may be clamped permanently at the correct
position of coupling.
(d) The type 106 receiving tuner circuits and adjustment are completely covered in para-
graph 138, Part IX.
(c ) Tuned Coil Emergency Transmitter. The student should note that the diagram, Fig.
261, contains the complete circuits of the Marconi tuned coil emergency transmitter. The
diagram includes the wiring of the induction coil and the charging panel.
When the left hand, two blade switch on the charging panel is closed, the main D. C.
line to the batteries is closed, but current will not flow through the batteries until the
plunger of the underload circuit breaker is pushed up by hand. If there are no loose con-
nections in the charging circuit, the plunger will remain in this position until the charging
current is cut off or until the voltage of the generator drops below that of the batteries
(note position of these switches in Fig. 205a, Chapter 10).
In order to take readings of the battery voltage, a small strap key placed alongside the
underload circuit breaker must be closed.
244
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
When the right hand double pole double throw switch is thrown to the upper set of con-
tacts, the transmitting key is connected in series with the power transmitting set, but if
thrown in the opposite position the key is in series with the primary circuit of the induction
coil.
To place the coil transmitter into operation, the flexible plug contact attached to B
should be removed from A and connected into C.
The arm of the rotary gap should be stopped in such position that a gap of the correct
length is provided for the induction coil.
The student should also trace out (in this diagram) the circuit of the rotary-gap motor
which includes the two-blade starting switch and the series rheostat. In practice the rheostat
is adjusted until a clear musical tone is obtained at the gap.
The motor starter shown in this diagram is the standard General Electric Company's
hand starter, the circuits of which are fully shown in Fig. 72.
197. Type "E-2" One-Half Kilowatt, 120 Cycle Panel Transmitter.— A
number of vessels in the American Mar-
coni service are equipped with *^> k. w.,
120 cycle panel transmitters fitted with
a quenched gap but unlike the type
"P-4" and type "P-5," this set is de-
signed for the two standard wave-
lengths only, namely, 300 and 600
meters. For emergency use, a rotary
spark gap is mounted on the end of the
motor generator shaft, which may be
used in place of the quenched gap when-
ever required. A complete circuit dia-
gram of the type "P" set appears in
Fig. 263, a front view in Fig. 264 and
rear views in Figs. 265 and 266.
A number of spare parts, such as an extra
motor generator armature, motor blower
armature, quenched gap plates, condenser
jars, etc., are supplied, positively insuring
against all possibility of breakdown.
198, Details of the Circuits and
Apparatus. — Explanation of the de-
tailed wiring diagram shown in Fig. 263 fol-
lows :
The. motor generator is of the Eck type,
having a two pole shunt wound motor and a
simple shunt field winding for the generator.
The speed of the motor is regulated by the
sliding contact rheostat R and the voltage of
the generator altered by the rheostat R-l. The generator field circuit may be broken by the
small switch shown in the drawing. The receiving apparatus is thus protected from 'hum-
ming" noises due to induction from the A. C. generator circuit.
The motor starter is the Cutler-Hammer single step type and is constructed somewhat
differently than the types employed in the 2 K. W. and % K. W. 500 cycle panel transmitters.
When the main D. C. line switch is closed, the resistance coil S is connected in series with
the D. C. armature. Owing to the almost complete absence of counter electromotive force,
the potential difference across the terminals of the armature at the start of the motor is
low; hence insufficient current flows through the solenoid windings W to draw up the
plunger P. As the speed of the armature increases, the counter electromotive force rises,
and accordingly the difference of potential increases ; finally sufficient current flows through
the solenoid W to draw up the plunger P, whereupon the contacts C and C-l are short-
circuited, shunting the resistance coil S out of the circuit. The motor is now connected
directly to the D. C. line.
The plunger P also separates the contacts D and D-\ connecting the resistance coil 5-1
in series with the winding W to protect the latter from overheating or burning out.
Fig. 264 — Front View of the Marconi l/2 K. W.
120 Cycle Transmitter.
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
245
AERIAL TUNING
INDUCTANCE
The transformer of the closed core type is denoted by the primary winding T and the
secondary winding T-l. Just previous to pressing the key, the voltage of the generator is
about 300 volts, but immediately drops to approximately 110 volts when the primary circuit
of the transformer is closed. The secondary voltage of the transformer with the con-
densers in shunt is about 14,700 volts. A safety discharge gap is connected to the secondary
winding terminals for the protection of the condensers and transformer in case one of the
leads from the regular discharge gap should become disconnected.
The wattmeter of the ordinary switchboard type— range 0-750 watts— is connected in the
circuit from the alternator to the transformer primary. The resistance coil N placed in
series with the potential coil of the meter is mounted at the front base of the switchboard.
The condensers are of the tubular Leyden jar type plated inside and outside with copper.
The average capacity of each jar is .0015 mfd. The actual value is accurately measured and
marked directly on the glass of each jar. In case of puncture a condenser jar of like
capacity must be substituted. The seven Ley-
den jars connected in parallel give a total
capacity of about .011 mfd. The inside and
outside terminals of the condensers are con-
nected directly to the secondary winding of
the transformer.
The oscillation transformer consists of a
primary and secondary winding of the pancake
type, which are indicated at L and L-l re-
spectively. Each winding consists of a single
coil of copper ribbon properly mounted and
spaced on an insulated base.
The secondary winding L-l, mounted on a
movable base, permits the coupling between it
and the primary winding L to be quickly and
easily adjusted.
The wave-length changing switch, operated
by the handle H, has two single blade contacts
which when thrown to the right simultaneous-
ly connect such values of inductance in the
antenna circuit and closed oscillation circuit as
to give each circuit a period corresponding to
600 meters. When thrown to the left both
circuits are given a wave-length of 300 meters,
provided the short-circuiting switch of the
short wave condenser X is open.
The correct number of primary and second-
ary turns for the 300 and 600 meter waves are MOTOR
determined by means of a wavemeter and con-
nection therefor made through the flexible
connectors E and E-l. The taps on the sec-
ondary inductance are located in the same
manner. Two values of inductance for the
standard wave lengths are selected through the flexible conductors F and F-l.
The spark discharger is of the multiple plate series type (quenched gap), consisting of
fifteen plates giving fourteen gaps. No more than eight of these are generally required,
leaving a number of spares. The discharge plates are of copper carefully ground, presenting
an absolutely smooth and uniform sparking surface. The plates are separated by specially
treated fibre washers. Cooling is effected by means of a small direct current blower J. The
motor circuit includes a switch for starting and stopping purposes.
The synchronous rotary gap discharger Y is mounted on the end of the motor generator
shaft. The rotating member has six discharge electrodes, while the stationary electrodes are
two in number. The stationary electrodes may be shifted through a small arc, thereby
permitting a spark discharge for each alternation of the charging current. This produces a
discharge of uniform pitch having a musical characteristic. The group frequency of this set
is 240 sparks per second.
Fig. 265— Rear View of the Marconi ]/2 K. W.
120 Cycle Transmitter.
246
PRACTICAL WIRELESS TELEGRAPHY.
c
The aerial tuning inductance of the continuously variable type, represented at L-2, is con-
nected in series with the earth lead and consists of a single spiral of copper ribbon having a
sliding contact U which allows connection to be made at any point on the spiral.
The aerial changeover switch for shifting the antenna from the sending to the receiving
apparatus consists of a single blade double throw switch. When thrown to the right, the
antenna is connected directly to the terminals of the receiving tuner ; when thrown to the
left, connection is made direct to the secondary winding of the transmitting oscillation trans-
former. These sets may be supplied with the type S, S, H, or I aerial changeover switch
as well.
The aerial ammeter of the Roller-Smith type, having a range of zero to 10 amperes, is
permanently connected in the aerial circuit and is used for obtaining the maximum value of
current and to indicate conditions of resonance between the open and closed oscillation
circuits.
The short wave condenser is of the standard Marconi type and may consist of either four
flat plates of glass connected in series or four
Leyden jars connected in series, giving a re-
sultant capacity of .0005 mfd.
The low potential power circuits are pro-
tected from electrostatic induction by pro-
tective condensers of large capacity. Two of
these condensers are connected in series and
earthed at the middle point. These protective
units are connected across the generator field
windings, the motor field windings, the arma-
ture of the blower motor and the alternating
current armature. The frame of the motor
generator is connected directly to earth.
199. General Instructions for Tun-
ing and Adjusting. — The following
general instructions should be carefully
observed by inspectors and operators:
(a) Regulation of Voltage and Frequency.
Connect the D. C. line (110-120 volts) to the
lower terminal of the fused switch marked
"D. C. Line," the aerial to the binding post
marked "A" on the back of the antenna change-
over switch and ground either one or both of
the terminals of the iron frame which sup-
ports the panel.
The slider of the generator field rheostat
should be placed near the lower end, the an-
tenna switch turned to "Send" position and
about eight or nine gaps of the quenched gap
connected in the circuit.
Next observe that none of the leads be-
tween the double two-point wave length switch
and the oscillation transformer are discon-
nected. Close the D. C. line switch which starts
the motor generator through the automatic starter. Then close the "generator field" and
the "blower motor" switch; finally close the "A. C. line" switch.
(6) Tuning. The complete set is now ready for tuning. Disconnect the antenna and tune
the closed oscillatory circuit to the desired wave length by means of a wavemeter.
Set the two-point switch indicator at "300."
Adjust the tap leading from the front coil of the oscillation transformer to switch point
marked "300" to the 300 meter wave length. Then turn the indicator to "600" and adjust the
tap to the higher wave length.
Next connect the set with the antenna, tune the secondary or open circuit to the closed
circuit and locate taps for each of the two standard wave lengths.
The coupling as well as the sliding contact which travels over the turns of the aerial
tuning inductance, should be varied while locating the wave-length tap, to find the best posi-
Fig. 266— Rear View of the Marconi
120 Cycle Transmitter.
K. W.
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
247
tion of both the coupling and flexible connection. The circuits are in resonance when the
aerial ammeter shows the highest possible reading.
With the average ship's aerial it is possible to locate the correct number of turns at the
secondary winding of the oscillation transformer so that the radiated wave can be changed
from 600 meters to 300 meters by simply throwing the changeover switch to the proper posi-
tion. When this switch is in the 300 meter position, the short wave condenser which is placed
in series with the earth lead must have its short-circuiting strap removed. Generally speak-
ing, the aerial tuning inductance tap is placed at a fixed point for either the 600 meter or 300
meter wave.
(c) Adjustment of the Spark Note. Either a receiver or a wavemeter may be used to indi-
cate the quality of the note. If the note is not clear vary the generator voltage, the number
of gaps and the transformer coupling, until it is clear or has a pitch of about 240 sparks per
Fig. 266a— 2 K. W. 240 Cycle Motor Generator With Synchronous Disc Discharger.
second. If the generator voltage is too high or too low, the note will either be rough or
else have the wrong pitch. The note may also be judged by the tone of the brush discharge
of the condensers.
Maximum antenna current does not indicate maximum efficiency. The note must also be
kept clear and the gap not worked above the antenna current at which the clearness is not
maintained.
The wattmeter should indicate about 500 watts and the number of gaps used should be
between eight and twelve.
The power of the set varies in the square of the number of gaps ; that is, if the ten gaps
represent full power the power would be 102 = 100.
The set is designed to carry a load of 500 watts. Any overload is liable to develop volt-
ages that may break down the condensers or cause trouble elsewhere in the set.
(d) Adjustment of the Quenched Gap. The quenched gap should not be taken apart until
absolutely necessary. When the circuits are in resonance, but the antenna current is less than
5 to 7 amperes or the wattmeter reading falls below its usual value, or when unable to get a
clear note, the gaps should be opened and the spark surfaces examined.
If the gap becomes short-circuited it can be determined by the use of the "gap tester"
(an insulated rod having a brass piece inserted in one end), which will indicate no 'spark
when bridged across two adjacent spark discs.
To open the gap, loosen the set screw in the left hand of the gap with a wrench which is
supplied with the set. Then lift out the plates.
248 PRACTICAL WIRELESS TELEGRAPHY.
If the plates and gaps stick together take care when forcing them apart not to injure the
gasket or the sparking surfaces. Should the gasket become injured or cling to the metal,
clean the plate off carefully and insert a new gasket.
The sparking surface of the plate should have a light, pink color with a somewhat dull
finish. If a plate has a rough, black appearance, it indicates that the gap was not airtight and
the sparking surfaces should be carefully cleaned with a very fine emery cloth.
Do not operate the set unless the blower motor of the gap is running, otherwise the heat
may destroy the gaskets. Never touch any circuit which may be alive without first opening
the field switch or the generator main switch, or possibly both.
200. Marconi 2 K. W. 240 Cycle Transmitter. — A number of vessels in the
Marconi service are fitted with a Z k. w. synchronous spark transmitter consisting
of several isolated instruments mounted on an operating table in a convenient
way.
The motor generator is a special Eck machine which takes current at the motor at 110
volts and generates current at 500 volts at frequency of 240 cycles. The motor is of the
interpole type which gives sparkless commutation and constant speed regulation under
variable load.
A synchronous rotary spark discharger, mounted on the generator shaft, consists of a
fiber disc carrying twelve spark points connected together by a copper strip. The stationary
electrodes, two in number, are mounted on a wooden muffling drum which encloses the disc.
Synchronous discharges are obtained by shifting the drum» carrying the stationary electrodes,
one way or the other, until a uniform spark note is secured. Simultaneous adjustments of
the generator voltage must be made noting the reading of the ammeter to insure that normal
power consumption is not exceeded. The complete motor generator and spark gap is
shown in Fig. 266a. The condenser may be either of the flat plate glass or copper-plated jar
. type. The oscillation transformer is the type mentioned in connection with the 1 k. w. 60
cycle sets and shown in the photograph, Fig. 119.
An open core transformer is employed taking current in the primary at 500 volts and
delivering at the secondary, current at pressure of 15,000 volts.
The receiving equipment may consist either of type 107a or a type 106 tuner connected to
a type I or type S. H. aerial changeover switch.
Either a General Electric Company or Cutler-Hammer Hand Starter may be supplied
with the motor generator.
Since the process of tuning of radio sets has been gone over repeatedly in connection
with other sets of the Marconi Company and particularly in paragraph 164, it is not deemed
necessary to repeat the instructions again. Briefly, the rotary gap is adjusted for a cleat-
spark note after which the closed circuit is tuned to the standard wave by a wavemeter and
the antenna circuit is adjusted to resonance by a hot wire ammeter or by the wavemeter if
desired.
201. Type P-9, ^ K. W. Cargo Transmitting Set.— One of the latest types
of transmitters developed by the Marconi Wireless Telegraph Company of America
is the type P-9 set which was primarily intended for cargo vessels or ships of
small tonnage.
Although the apparatus of this set is not placed on a panel board as the types
P-4 and P-5, the component parts are mounted in a convenient way in an angle
iron frame as shown in the photographs, Figs. 266-b and 266-c. Fig. 266-d is a
complete wiring diagram of the set.
It is to be noted first that the lower part of the frame holds the motor generator, the high
voltage condenser and a step-up closed core transformer.
On the upper shelf is placed the oscillation transformer, the aerial tuning inductance, the
short wave condenser, the lightning switch and a resonance indicator for purposes of tuning.
A hand-operated motor starter is mounted to the side of the panel and immediately under-
neath a terminal board for making connections to the power mains, the aerial changeover
switch and the telegraph key.
This set was designed with the utmost simplicity of construction and operation in view
and is one that can be placed in unskilled hands without fear of breakdown.
Unlike the Marconi transmitters previously described, type P-9 is not fitted with a
variable field resistance or an aerial ammeter. Fixed resistance coils are connected in series
with both the motor and generator field windings and conditions of resonance between the
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
249
open and closed oscillation circuits are determined by a small glow lamp shunted by a semi-
loop of wire. It is to be observed also that the coupling between the primary and secondary
windings is changed by moving the primary at right angles to the secondary.
(a) Description of the Set. The motor generator is a ^ K. W. 500 cycle machine of the
Crocker-Wheeler type, the load voltage of the alternator being about 120 volts.
OSCILLAT10H
HOTARY GAP
CLOSED CORE
TRANSFORMER
Fig. 266b— The Marconi y4 K. W. Cargo Type Transmitting Set Complete.
The motor has a differential field winding for maintaining a constant speed under variable
load and it is designed for connection to a 110 volt direct current circuit.
The motor starter is one of the Industrial Controller Company's hand-operated type with
the usual connections to the motor. (See wiring diagram, Fig. 266-d.)
Protective V? microfarad condensers are attached to the motor generator circuits to
neutralize any differences of potential that may be set up by the transmitter. One terminal
of these condensers is connected to a binding post of the machine and the other terminal to
the frame of the motor generator, which, in turn, is thoroughly connected to earth.
The high voltage transformer is one of the closed core type (Fig. 266c), which is im-
250
PRACTICAL WIRELESS TELEGRAPHY.
mersed in a semi-liquid grease. A small fixed reactance coil is connected in series with the
primary winding for regulation of the current.
The high voltage condenser consists of two small sized copper-plated jars of .001 micro-
farads each, which are shunted across the secondary terminals of the transformer.
The oscillation transformer has two flat spiral coils made of copper strip wound edgewise,
the primary winding being connected in series with the spark gap circuit and the secondary
winding in series with the antenna circuit. The correct number of turns in either winding
AERIAL TUNING
INDUCTANCE
SECONDARY OSCILLAllOli
TRANSFORMER
PRIMARY
•L,
TERMINAL
BOARD
Fig. 266c — The Marconi J4 K. W. Cargo Set showing the General Arrangement of
the Apparatus.
for the standard waves is obtained by means of a small clip contact attached to a flexible
lead. The positions of the 300, 450 and 600 meter waves at the primary winding are clearly
marked and the contact clip must be shifted by hand for each change of wavelength.
The aerial tuning inductance also consists of a flat spiral copper strip wound edgewise
on an insulating base, the inductance being varied by a flexible lead and contact clip.
Instead of an aerial ammeter, a resonance indicator is connected in series with the
antenna circuit. It consists of a small glow lamp shunted by a loop of wire upon which
bears a sliding contact. By regulating the length of the shunt circuit, the proportion of
current flowing through the lamp can be carefully regulated.
STANDARD MARINE SETS OF AMERICAN MARCONI CO.
251
The short wave condenser consists of two .001 microfarad condensers connected in series
which are shunted out of the circuit by a knife blade switch. This switch also connects the
aerial to earth for protection against lightning.
The type I aerial changeover switch furnished with this set is fully described in Para-
graph 155. This switch in the transmitting position:
(1) Closes the alternating current circuit to the transformer;
(2) Closes the field circuit to the generator;
(3) Disconnects the aerial from the receiving tuner primary;
(4) Places the detector, head telephone and secondary of the receiving tuner
on short circuit.
Fig. 266d— Complete Wiring Diagram of the *A K. W. Cargo Transmitting Set with Type 112 Receiving
Tuner and Type I Aerial Changeover Switch.
In the receiving position the reverse operations are performed.
The remainder of the type P-9 equipment comprises a type C transmitting key, type 112
receiving tuner and a pair of 2,000 ohms D. H. receivers.
In addition, lead-covered wire, rubber-covered wire and copper tubing is supplied for
connecting up the apparatus.
The type 112 receiving tuner is described in detail in Paragraph 156.
(fc) Installation. The main D. C. line to the motor generator and hand starter is inter-
rupted by a 30 ampere knife blade switch which is fused for 20 amperes. This is placed in a
position convenient to the operator.
The blades of the switch are connected to studs No. 1 and No. 2 of the terminal board
with No. 14 lead-covered wire. Stud No. 3 of the terminal board connects to one terminal
252 PRACTICAL WIRELESS TELEGRAPHY.
of the type C key; the other key terminal connects to terminal No. 12 of the type T switch.
Terminal No. 11 (type I switch) connects to stud 6 of the terminal board. .
Stud No. 4 of the terminal board connects to terminal No. 10 of the type I switch.
Terminal No. 7 of the type I switch connects to stud No. 5 of the terminal board.
In order to conduct induced currents to earth, the lead coating of the wires is thoroughly
connected to the earth wire.
The antenna lead-in insulator is connected to the type I switch contact marked "ANT
C'K'T" by means of quarter-inch copper tubing.
The type' I switch contact marked "OSC C'K'T" is connected to the switch blade terminal
of the short wave condenser.
All other connections to the type I switch are firmly soldered in special lugs provided for
the purpose. The copper tubing is supported by two standard lighthouse type of insulators
supplied by the Marconi Company.
The ground stud on the frame work of the transmitting apparatus is connected to earth
by a zinc strip one-half inch in width.
Terminal No. 1 of type I switch is connected to binding post marked "Aerial" or "ANT"
on the receiving tuner.
The tuner binding post marked "Ground" or "GND" is connected directly to the earth.
The left telephone binding post is connected to the terminal No. 5 of the type I switch.
The right telephone binding post is connected to terminal No. 2.
On the type 112 receivers with serial numbers from 2 to 13 inclusive, the. small binding
post marked "Detector" (located beside the primary tap switch) is to be connected to terminal
No. 4 of the type I switch; but on receiving tuners with serial numbers from 14 up, the
binding post marked "Detector" or "DET" opposite the telephone binding post is to be con-
nected to terminal No. 4 of the type I switch.
The three dry cells are connected to the battery binding posts on the receiver as shown in
Fig. 266d. The receiving apparatus is connected with No. 18 rubber-covered solid wire.
(c) Adjustment. After the transmitting set is connected to the power mains, aerial switch,
etc., the first adjustment is to be made at the electrodes of the rotary gap.
(1) Lower the stationary electrodes by unscrewing the adjusting nut at the
top (one at a time) until they touch the electrodes on the disc; then turn
the adjusting screw to the right until the electrodes just clear those on
the rotary disc, when the latter is turned over by hand. The proper
separation is from .005 to .01 of an inch. Be sure that the engaging pin
on the stationary electrode is properly seated.
(2) Next close the main D. C. line switch and start the motor generator by
drawing the starting handle over slowly.
(3) Close transmitting key and shift the muffling drum carrying the stationary
spark electrodes until the note is clear and musical.
(d) Tuning. The set is tuned to the three standard waves as follows:
(1) Set contact clip on the primary coil of the oscillation transformer at the
desired wave length (the position of the tap for each of the three standard
waves is plainly marked on the coil).
(2) To insure accuracy, check back the wave length of the closed oscillation
circuit by a wavemeter.
(3) Set the primary coil of the oscillation transformer at an angle of about 50°
to the secondary.
(4) Cut in 4 or 5 turns at the secondary winding.
(5) Add turns at the aerial tuning inductance until the resonance indicator
glows brightly.
(6) If glow lamp becomes excessively incandescent, turn the small shunt
switch counter clockwise.
(7) Continue changing the antenna inductance until the indicator shows a
sharp maximum.
(8) Then draw the primary winding further away from the secondary and
slightly retune the antenna circuit.
(9) The set generally will be properly tuned when a slight change in coupling
or antenna inductance causes a decrease of the antenna current.
(10) If the coupling proves too close with the primary winding at right angles
with the secondary, cut out turns in the secondary and add turns at the
aerial tuning inductance until resonance is obtained.
STANDARD MARINE SETS OF AMERICAN MARCONI CO. 253
When connected to aerials having natural wave lengths between 250 and 300
meters, these sets will give antenna current of from 3 to 4 amperes, which will
permit communication over several hundred miles.
202. Aerial Current and Reduction of Power. — In order to familiarize
operators with the approximate values of aerial current to be expected from the
different Marconi transmitters at the three standard waves, the following table
is appended. Different values will be obtained with different aerials but those
given may be considered as a good average :
Type of Transmitter. 300 meters. 450 meters. 600 meters.
2 K. W. 500 cycle 3 to 5 amperes 9 to 13 amperes 12 to 17 amperes
y^ K. W. 500 cycle 2 to 4^ amperes 5 to 7 amperes 5^ to 8 amperes
1 K. W. 60 cycle \y2 to 3 amperes 5 to 7 amperes
Y2 K. W. 120 cycle \y2 to 3 amperes 5 to 7 amperes
2 K. W. 240 cycle 1 *%, to 3 amperes Sy2 to 8 amperes
y4 K. W. 500 cycle 1 to 2 amperes 3 to 4 amperes
(a) Reduction of Power. The International Regulations require that the
transmitter be constructed to permit the power to be reduced progressively from
maximum to zero. The United States regulations permit the power to be reduced
in certain types of sets by reduction of the coupling between the primary and
secondary windings, which reduces the antenna current.
In the quenched gap sets, the power is reduced ( 1 ) by cutting out the gaps,
(2) by reduction of the generator voltage or (3) by lowering the coupling if
necessary. The power of the synchronous spark sets is reduced by reduction of
the coupling between the primary and secondary zvindings of the oscillation trans-
former (thereby reducing the antenna current) or by lowering the generator
voltage.
In order to secure a uniform spark discharge under reduced power, it may
be necessary with synchronous spark sets to slightly readjust the position of the
stationary electrodes.
Certain types of transmitting sets are provided with primary or secondary
reactance coils which reduce the primary or secondary current to a minimum
value, but there is an objection to reducing the power in this way because a total
readjustment of the gap and secondary voltage is required for clear tones.
In sets like the Marconi 2 K. W. 240 cycle transmitter or the 1 K. W. 60 cycle
transmitter, the antenna current is reduced by turning the secondary winding of
the type A oscillation transformer at right angles to the primary winding or at
any intermediate position. (See curve Fig. 245A).
203. General Instructions for the Panel Sets. — Operators in the Marconi
service are urged to give careful attention to the following general instructions
for the care and maintenance of the panel transmitters :
(1) Observe the oil containers of the generator and motor bearings frequently
and keep them well supplied with oil. Open small petcock occasionally
for test.
(2) Keep close watch on the spring contacts of the aerial changeover switch
for looseness of contact.
(3) Wipe the insulating rods of the panel board frequently with a slightly
oiled cloth to prevent the accumulation of dust or moisture.
(4) Make daily test of the reading of the aerial ammeter. Vary the in-
ductance of the aerial tuning inductance slightly to compensate for vary-
ing sag of the wires.
(5) Make daily test of the auxiliary battery or auxiliary set. Keep batteries
fully charged.
(6) Tighten up all nuts and bolts on the panel board frequently.
(7) Take up the adjusting nut on the quenched gap a fraction of a turn now
and then.
(8) Keep brushes on the motor clean.
254 PRACTICAL WIRELESS TELEGRAPHY.
(9) Keep close watch on the dead-end switch spring contacts of the receiving
tuner. Also keep metal sectors on the rubber rod and the brushes clean.
(10) If aerial ammeter burns out, disconnect it completely from the thermo
couple. If necessary place a shunt around the heater terminals.
(11) If the resistance coils in series with the solenoid windings burn out,
substitute two 16 C. P. lamps connected in parallel. Should the plunger
on the automatic starter not rise when the starting switch is closed, raise
it by hand and block it in position with a stick of wood, for temporary
operation. At an opportune time examine the resistance coil in series
with the solenoid winding.
(12) Oil bearings and gear wheels of wave length and coupling adjustment
with a few drops of thin oil.
(13) In so far as possible protect set from moisture at all times. When
sparking takes place at the safety gap, readjust rotary gap or use less
plates at the quenched gap.
(14) Do not under any circumstances exceed the power rating of the set.
(15) For broad interfering wave use close coupling and full power input.
Although the circuits and description of the various parts of a complete panel
transmitter when treated in detail may appear rather complicated to the beginner,
he should bear in mind that these senders are entirely automatic in operation.
In fact, during practical operation, in order to change the apparatus from a
transmitting to a receiving position, the operator is only required to shift the
position of the antenna changeover switch.
Moreover with the panel sets, the length of the radiated wave can be instantly
changed from one to the other of the three standard waves (300, 450 and 600
meters) by merely throwing a switch.
One skilled in the knowledge of telegraphy could learn to manipulate a
transmitter and receiver within a day's practice, but more detailed knowledge of
the circuits is required on the part of the operator, in order that he may be able
to cope with such troubles as may arise at sea.
PART XIII.
MARCONI DIRECTION FINDER OR WIRE
LESS COMPASS AND ITS
APPLICATION.
204. IN GENERAL. 205. DESCRIPTION OF EQUIPMENT. 206.
THE DIRECTION FINDER AERIALS. 207. THE CIRCUIT COM-
PLETE. 208. THE TUNED BUZZER TESTER. 209. How CUR-
RENT Is INDUCED IN THE LOOPED AERIALS. 210. DIRECTION
OF MAGNETIC FORCES WITHIN THE GONIOMETER. 211. GEN-
ERAL INSTRUCTIONS FOR OPERATION OF THE DIRECTION FINDER.
212. To FIND THE DIRECTION OF A RADIO STATION.
204. In General. — The radiogoniometer or direction finder is a specially
designed receiving apparatus for determining the direction of a wireless tele-
graph transmitting station at a given receiving station. The device was primarily
intended as an aid to navigation, enabling the officer of a vessel to make observa-
tions and establish his position independent of weather conditions, such as fog,
etc. It is applicable in many other ways also and can be employed to advantage
by armies and navies ; by means of it a hostile wireless station may be definitely
located, or the direction of the enemy's
battleships while in radio communica-
tion, "sensed."
Government inspectors are likewise
enabled to "round-up" interfering ama-
teur stations by using the direction finder.
The apparatus is even of considerable
value for ordinary receiving purposes
(short range work), for it allows the re-
ceiving operator, when the ether in a
given locality is congested, to "screen out"
unwanted wireless telegraph signals.
The Marconi direction finder is an
adaptation of the apparatus originally
evolved by Messrs. Bellini and Tosi ;
however, the device as produced by
these inventors was not adapted to
ship work. Improvements were made
by the Marconi Company and equip-
ment is now turned out in a form en-
tirely satisfactory for use by naviga-
tors, giving, as it does, a high degree
of accuracy.
205. Description of Equipment. — The complete equipment consists of a
goniometer with the necessary appliances for control as in Fig. 267, a tuned imre-
less telegraph receiver shown in Fig. 268, a tuned buzzer tester as in Fig. 269,
and an angle divider as in Fig. 270.
Fig. 267 — The Radio Goniometer.
256
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 268 — The Tuned Receiver for the Direction
Finder.
206. The Direction Finder Aerials.— A distinctive feature of the direction
finder equipment is the use of two closed circuit looped aerials having the form
of an isosceles triangle as shown in Fig. 271. These aerials bisect each othfer at
right angles and also hold an angle
of 45° with the bow and stern line
of the vessel.
It is important that the aerials be
placed in a somewhat clear space on the
deck and that the two loops have identical
dimensions. The wires should be held
taut and firmly in place. The current col-
lected by the aerials, from the advancing
electromagnetic waves, is made to flow
through a specially designed set of excita-
tion coils, setting up a magnetic field which
acts upon a third coil known as the ex-
ploring coil. The latter coil carries a
pointer which moves over a 360° scale and
gives the sense of direction of any trans-
mitting station. This portion of the ap-
paratus is known as the goniometer, the
windings for which are clearly shown in
the photograph, Fig. 272. It will be re-
ferred to again hereafter.
The sketch, Fig. 273, is a plan view of the two triangular aerials as previously described,
showing their relative positions to the bow and stern line of a given vessel (marked B
and S).
Before entering into a detailed explanation of the circuits, the diagram in Fig. 274
should have consideration. Let A and B represent two sides of a single loop of the direc-
tion finder aerial, and the arrows, the direction of the flux in a passing wireless wave ;
then, this loop receives the maximum induction when its plane bears the position, to the
passing wave, shown. Furthermore, a little study of the diagram will show that the current
set up by this flux in side A, is in op-
position to that set up in side B ; but if
the two sides of the loop are spaced a
certain distance apart, the current in-
duced in side B will attain maximum
amplitude an instant later than in side
A; hence, an electric current, the re-
sult of the two E. M. F.'s flows around
the loop A, B. The magnetic flux
generated thereby, in the coil L, acts
inductively upon the exploring coil L-2
the resulting oscillations being rectified
by the detector and associated appa-
ratus, and made audible in head tele-
phones in the usual manner.
It is plainly evident that both sides
Fig. 270 — Angle Divider.
Fig. 269 — Tuned Buzzer Tester.
DIRECTION FINDER OR WIRELESS COMPASS.
257
of the loop A, B, are acted upon equally and at the same instant when its plane is at a right
angle to the plane of the advancing wave. Equal and opposing electromotive forces will, there-
fore, be induced in both legs, resulting in no flow of current.
If, however, the loop A, B, is acted upon at any other angle than a right angle, an elec-
tromotive force will be
induced, the intensity of
which varies as the co-
sine of the angle which
the advancing flux
makes with the loop.
The description just
given does not take into
account the phenomena
involved when both
loops are employed and
the consequent effect on
the goniometer coil. This
will be explained in a
later paragraph. We
shall first proceed to a
description of the direc-
tion finder complete.
207. The Circuit
Complete. — Careful
inspection should be
made of the diagram of
connections in Fig. 275.
The triangular loop
aerial, A, B, is connected
in series with the vari-
able condenser K and to
the excitation coil L.
The loop aerial C, D, is
connected in series with condenser K-l and the excitation coil L-l. The condensers K and
K-l have identical values of capacity and their capacities are altered simultaneously by a
handle mounted on the top of the box as shown in Fig. 267.
TO RtCElVER
Fig. 271 — The Triangular Aerial Employed
Direction Finder.
in Connection
the
Fig. 272 — Detail of the Radio Goniometer.
Fig. 273— Diagram Showing the General Layout of
the Direction Finder Aerials.
258
PRACTICAL WIRELESS TELEGRAPHY.
The magnetic field produced by the coils L and L-l combine and act upon the exploring
coil L-2, the position of which will be more clearly understood from the photograph, Fig.
272, which also shows the rectangular coils to be connected to the loops of the aerial. The ex-
ploring coil is placed inside the antenna coils and is turned by the handle on the top of the set.
The oscillations induced in L-2 by the oscillatory current flowing in the coils L and L-l is
transferred to the inductance coil of the local detector circuit L-4 by the coil L-3.
The coil L-2, the variable condenser
V, and1 the coil L-3, constitute an inter-
mediate circuit similar to that employed
in the well-known Marconi valve tuner.
The coupling between the coils L-3 and
L-4 is varied by a knob mounted on the
side of the tuned receiver.
The detector circuit consists of the in-
ductance coil (of fixed value) L-4; the
billi-condenser V-l in shunt; the fixed
condenser V-2; the head telephones H;
the potentiometer P and the battery B.
Two detectors are employed for this set;
one a crystal of carborundum, the other
a crystal of cerusite; either one of which
may be connected in the circuit as de-
sired. When the cerusite detector is in
use, the battery and potentiometer are cut
out of the circuit.
208. The Tuned Buzzer Tester.—
The direction finder equipment also in-
cludes a tuned buzzer tester which may
be set to radiate waves either 300 or 600
meters in length. The buzzer box has
four holes, one in each corner, through
which the four leads from the two looped
aerials pass. These holes are marked S F
(Starboard Forward}, S A (Starboard
Aft}, P A (Port Aft} and P F (Port
Forward}. Care should be taken to bring
the corresponding leads from the loop
aerials through the proper holes. The
leads for both aerials are now in inductive
relation to the tuned buzzer circuit ; hence,
the aerials and in fact the entire apparatus may be preadjusted to the two standard wave
lengths, assuring that a sender transmitting on one of these waves will be heard.
It is sufficient for the time being to say that for the practical operation of the apparatus,
the aerial circuit, the intermediate circuit, and the local detector circuit must be accurately
tuned to resonance and to the incoming waves. The exploring coil is then turned on its
axis until the maximum strength of signals is secured in the head telephones. The pointer
on the coil L-2 will then lie in the direction of the transmitting station.
We shall now explain the induction of current in the two looped aerials by an advancing
electromagnetic wave.
209. How Current is Induced in the Looped Aerials. — If the waves from
a given transmitting station, Fig. 273, advance in the general direction E, oscillating cur-
rents will be induced in the loop C, D, but none in loop A, B. To obtain the maximum
induction from these oscillations, the exploring coil must, in this case, lie parallel to the
goniometer excitation winding connected to the terminals of the loop C, D.
Again, if the waves advance in the direction E-l, the induction on the loop A, B is maxi-
mum and on C, D nil. Hence, the exploring coil must now lie parallel to the goniometer
winding connected to the loop A, B to receive the maximum induction, and the pointer will
lie along the direction E-l.
If the waves advance in the direction E-2, both loops are acted upon simultaneously and
vOOQOQ
a Single Loop
DIRECTION FINDER OR WIRELESS COMPASS.
259
AERIALS
TUNED BUZZER CIRCUIT
CARBORUNDUM
Fig. 275 — Complete Wiring Diagram of the Marconi Direction Finder,
260 PRACTICAL WIRELESS TELEGRAPHY.
equally, and an oscillatory current flows through both excitation windings of the goniometer.
The magnetic fields set up by the two coils combine and produce a resultant Held from
which the maximum induction will be obtained in the detector circuit, when the pointer of
the exploring coil lies parallel to a line drawn midway between C and D, A and B (dotted
line).
But let the waves arrive in the direction E-3 ; in this case the loop A, B will receive the
maximum induction of the advancing wave while the loop C, D will be acted upon feebly.
To obtain the maximum induction from the resulting magnetic field, the goniometer coil
will be in such position that the pointer will lie along the direction E-3.
210. Direction of Magnetic Forces Within the Goniometer. — Figs. 276 and
277 outline the production of the magnetic field within the goniometer when both aerials
are acted upon by the advancing wave simultaneously. It should be remembered that in
order to induce the maximum current in the detector circuit, the exploring coil is always
at right angles to the magnetic field within the goniometer windings. This is shown in
the diagram, Fig. 276, which is in fact a plan view looking down from the top on a single
coil connected to one of the loop aerials. The direction of the magnetic lines of force with
a given direction of current and the corresponding position of the exploring coil for maxi-
mum induction is clearly mapped out as well as the position of the pointer on the scale and
its mounting relative to the coils.
Fig. 277 is a plan view looking down from the top on the two coils of the goniometer
showing, by the dotted lines, the resultant magnetic field when both aerials are acted upon
simultaneously and with equal intensity. If current flows in the coil A, B only and in the
direction shown, the corresponding magnetic lines of force will take the general direction
of the heavy lines (the N and S polarity being as indicated). And again, if only the loop
C, D is acted upon by the advancing waves, then the general direction of flux in the
corresponding goniometer coil will be that shown. But when current Hows in both coils at
the same time, it is clearly seen that the corresponding fluxes are at right angles and a
resultant field is produced which will take the paths F and F-\ and the pointer on the coil,
for maximum induction, will lie in the direction P and P-l. The exploring coil must, there-
fore, be in the position shown to receive the maximum induction from the resultant mag-
netic field.
211. General Instructions for Operation of the Direction Finder. — (1) As
a matter of convenience, the box containing the goniometer coils and the variable condenser,
should be so placed that the zero position on the scale coincides with the bow and stern line
of the vessel.
(2) The tuned buzzer circuit is then set into operation at either 300 or 600 meters, de-
pending upon which wave-length it is desired to receive.
(3) The coupling knob on the tuned receiver is turned to 90°.
(4) With the buzzer in operation, the condenser connected1 across the intermediate
circuit and the billi-condenser are altered in capacity (simultaneously adjusting the de-
tector) until maximum response is secured in the head telephones.
(5) When the foregoing adjustments have been made, the capacity of the condenser in
the antenna circuit is altered by the knob on the top of the goniometer box until a still
greater response in the head telephones is obtained. It may then become necessary to
slightly readjust the values of capacity in use at the intermediate circuit condenser and the
billi-condenser.
(6) When the two loop aerials are in use and the buzzer is in operation, the loudest
signals are obtained from the buzzer when the pointer is at zero. The signals should
gradually decrease in strength as the pointer is moved toward the 90° position.
(7) When the two aerials are in use, zero signals should be obtained when the pointer
is in the position 90°-90e.
(8) When one of the aerial loops is disconnected by means of the switch on the top of
the goniometer box, the maximum signal is received with the pointer at 45°-135° in one
direction and the zero signal with the pointer 45°-135° in the opposite direction. The re-
verse condition takes place when the second loop is in use alone.
(9) If, when the loops are thus tested singly, it becomes necessary to alter the capacity of
the intermediate or the billi-condenser for maximum response, it is a positive indication
that the loops are unsymmetrical and therefore out of balance. Identical positions of con-
denser capacity should be obtained on both loops. Steps should be taken immediately to
DIRECTION FINDER OR WIRELESS COMPASS.
FLUA
261
Fig. 276 — Showing the Magnetic Flux Within a Single Coil of the
Goniometer Under Given Conditions.
TO AERIAL
EXCITATION COIL
DIRECTION OF
ADVANCING
WAVE
&
TO AERIAL
Fig. 277— Showing the Resultant Flux Set Up in the Two Excitation Coils
of the Goniometer.
262 PRACTICAL WIRELESS TELEGRAPHY.
correct this error which undoubtedly lies in the aerial. A slight compensation for this un-
symmetrical condition may be made at the variable condensers insid'e the box by means of
two small adjusting screws.
(10) The 'strength of the signals in one loop should be identical with that in the other.
If not, a bad connection probably exists in one of the aerials.
212. To Find the Directions of a Radio Station. — (1) The station whose
direction is to be determined if not already in the act of sending, should be called and
requested to send a test letter for two or three minutes, making sure to disconnect the two
looped aerials of the direction finder by switches mounted on the top of the goniometer
box during the sending period.
(2) When a reply is received (on the ordinary receiving equipment), the ship's trans-
mitter and receiver are put out of action, even to the disconnecting of the flat top aerial
from the earth, which, if left in the circuit, will seriously affect the accuracy of the goni-
ometer reading.
(3) Next close the two switches for the loop aerials and swing the direction finder
handle until the maximum strength of signals is obtained in the head telephone. This should
not be a difficult adjustment, as the apparatus has prevoiusly been adjusted to the maximum
degree of sensitiveness and to the standard wave length adjustment by means of the test
buzzer. The pointer will now indicate on the goniometer scale the general direction of the
transmitting station from which signals are being received, that is to say, it shows the
direction with respect to the bow and stern line of the vessel.
(4) If the signals received are not sharply denned, having about equal strength over
a considerable portion of the goniometer scale, the positions should be noted where the
signals fall to zero (above and below maximum) and a mean of the two readings taken.
The mean reading is obtained by the angle divider furnished with the set.
(5) Before transmission is again resumed, care should be taken to disconnect the two
loop aerials from the goniometer by means of the switches previously described, and also
to put the detector switch at zero.
It should be understood that the direction finder only gives the sense of direc-
tion in reference to the bow and stern line of a vessel and not the geographical
direction of the wireless station, which, of course, must be obtained by the readings
of the standard ship's compass. More clearly, the direction finder gives the angle
which the advancing wave from the transmitting station makes with the center
line of the vessel.
For instance, if the pointer of the direction finder indicates that ±he general direction
of the transmitting station is 20° off the port bow, it does not show whether that station
is 20° to the port bow or 20° to the starboard quarter. In the case of land stations there
need be no doubt concerning this, as it is generally known whether the station is to the
port or starboard side of the vessel. There can never be much doubt as to whether a ship
is approaching or receding from a land station, for by the reverse interpretation, the land
station would be located at sea — an obvious absurdity.
//, in case of a heavy fog, the signals from another ship indicated that it bore a direc-
tion over the bow and stern line of the vessel, and the signals from the ship became o/l
gradually increasing intensity, it, of course, indicates that the ships are approaching each
other, but does not show whether bow-on, or in the same general direction. A wireless
message sent to the ship asking her course, would of course, remove all doubt and enable
the navigator to avoid a collision.
Readings may be taken simultaneously of two land stations, and the position of the
vessel located by well known navigation methods. Readings may be taken from a single
station and1 the ship moved forward in a straight course to a definite distance and a second
observation made. The data obtained in this manner is sufficient to establish the position of
the vessel.
An interesting application of the direction finder is the assistance it gives in locating a
distressed vessel in foggy weather or after darkness. After the distress signals have been
received1, the position of the distressed vessel transmitted and certain information given to
the relief vessel to enable the commander to know what direction he shall take, the distressed
vessel is then asked to make the test letter "V", or any other prearranged signal. The direc-
tion finder of the relief vessel is then put into operation and the general direction of the
signals of the distressed vessel obtained.
DIRECTION FINDER OR WIRELESS COMPASS.
263
The relief vessel is then swung by the helm until the bow and stern line of the vessel
coincide with the position of the pointer on the direction finder where maximum signals are
obtained. In this manner, the relief vessel can be kept on a direct course and the distressed
vessel located in the quickest possible manner.
When entering ports like New York harbor, where the atmosphere is at times congested
with wireless traffic, the direction finder has been employed in a most efficient manner for
eliminating unwanted signals. First one loop is thrown in the circuit; if the station desired
is not heard, the second loop is thrown in and a test made. If the signals are received on
this loop, 50 per cent, of the local interference under some conditions may be wholly elimi-
nated, or at least detuned to such an extent as to be negligible. Or, if desired, both loops
of the direction finder may be employed, and the pointer of the goniometer set in the direc-
tion of the station from which signals are being received. It is certain that in this direction
the maximum strength of signals will be received, and thos.e of all other stations not on the
same general line will be reduced or wholly excluded.
Under favorable conditions, bearings may be taken with the direction finder within two
or three degrees of accuracy ; the error due to the instrument itself does not exceed 1 degree.
The range of this apparatus with a carborundum detector is from 40 to 50 miles, but with a
cerusite detector it may be extended to 160 or 170 mile.s, which is ample for navigation
purposes.
The direction finder has been found applicable to the reception of long wave length
signals over great distances. Recent tests with this aerial were carried out by the Marconi
Wireless Telegraph Company of America, at their transatlantic receiving station, located
at Belmar, N. J., U. S. A. The direction finder loop aerials were erected on a 450-foot
mast, and the receiving apparatus designed to be responsive to waves inclusive of 10,000
meters. With a receiver responsive to undamped oscillations, daylight signals were re-
ceived from the Marconi Stations at Carnarvon, Wales, and Clifden, Ireland; also from
the German stations at Nauen, Germany, and Hanover, Germany. The direction of these
stations was readily found with a notable degree of accuracy.
Fig. 277a — The Direction Finder Complete with Fleming Oscillation Valve.
\
PART XIV.
TRANSMITTERS OF UNDAMPED
OSCILLATIONS.
ARC GENERATORS— RADIO-FREQUENCY ALTERNATORS—
PLIOTRON OSCILLATOR.
213. IN GENERAL. 214. THE ARC GENERATOR. 215. SIGNAL-
LING WITH THE ARC TRANSMITTER. 216. THE ALEXANDERSON
HIGH FREQUENCY ALTERNATOR. 217. GOLDSCHMIDT RADIO-
FREQUENCY ALTERNATOR. 218. THE JOLY SYSTEM FOR THE
PROTECTION OF UNDAMPED OSCILLATIONS. 219. MARCONI'S
SYSTEM FOR THE PRODUCTION OF CONTINUOUS WAVES.
220. THE PLIOTRON OSCILLATOR.
213. In General. — Progress in the United States in the development of
sustained oscillation generators has been particularly marked during the past few
years.
In fact, by the use of undamped wave apparatus the transmitting range of
high-power stations has been materially increased; and in view of the wide-
spread interest in continuous wave equipment, the fundamental circuits
and operation of some of the more important systems will be briefly described
and explained.
Sustained waves are defined as the waves radiated from a conductor in which alternating
current flows. The terms "undamped" "sustained" and "continuous" are often employed
synonymously and are presumed to indicate oscillations of continuous amplitude and constant
formation in contrast to "discontinuous" oscillations which occur in groups of 200 to 1,000 per
second, and are obtained by the recurring charge and discharge of a condenser across a
spark gap. A slight distinction in the use of these terms should be made, as electrical
oscillations may be continuous in the sense that they are not broken up into distinct groups
but the successive cycles may vary in amplitude, an example being the type of oscillations
generated by the arc.
Continuous waves are set into motion by:
(1) The radio-frequency alternator such as the Alexanderson and Goldschmidt
types.
(2) The Poulsen or Duddell arc generator.
(3) A battery of vacuum valve tube, such as the General Electric Pliotron oscil-
lators.
At the writing of this volume, marine wireless telegraph sets are fitted with discontinuous
wave transmitters, almost exclusively, but high power stations employ either continuous or
discontinuous wave apparatus. One reason why continuous wave transmitters have not been
universally adopted for ship service is accounted for by the fact that the apparatus for the
production of continuous oscillations (or waves) generally involves mechanical and electrical
problems difficult to surmount or else the apparatus is too intricate or cumbersome to be
installated aboard ship. It is therefore safe to predict that discontinuous wave apparatus will
be employed in this branch of radio communication for some time to come.
TRANSMITTERS OF UNDAMPED OSCILLATIONS.
265
214. The Arc Generator. — A simple system for generating continuous
oscillations is the arc generator, the circuits of which are shown in Fig. 278,
where an arc gap of copper and carbon electrodes A, B, is shunted to the terminals
of a 500 volt direct current dynamo. In this diagram C-l and C-2 are iron core
inductances which prevent the oscillations of radio-frequency discharging back
into the generator. C
is the usual con-
denser of the closed
oscillation circuit
and L the variable
inductance. In the
usual manner, the
oscillations generat-
ed in this circuit are
transferred to the
antenna circuit by
means of an oscilla-
tion transformer.
The functioning of
this apparatus is as
follows : When the
electrodes of the arc A, B, are first placed in contact and then given the correct separation,
considerable difference of potential exists across the terminals as can be shown by a volt-
meter. Accordingly a certain amount of current flows into the condenser C which receives
a charge. The charge taken by the condensers robs the arc of some of its current, which
JIM;
iron
Fig. 278— Fundamental Diagram of the Poulsen Arc Generator.
(oooiooooo/
Fig. 279 — Complete Circuits of a Modern1 Arc Transmitter.
further increases the potential across the arc and places a still greater charge on the con-
denser. When fully charged, the condenser discharges across the arc gap and lowers the
arc voltage. This decrease of arc voltage also assists the discharge of the condenser mate-
266
PRACTICAL WIRELESS TELEGRAPHY.
rially and due to the inertia of the oscillation circuit, the condenser will continue to discharge
in the opposite direction, or, in other words, an alternating current will flow through the
oscillation circuit. Due to the fact that direct current is constantly supplied to the arc and
condenser, this process of charge and discharge continues so long as the arc is in operation,
and the resultant frequency of oscillation is approximately that due to the inductance,
capacity, and resistance of the condenser circuit. The oscillations flowing in this circuit
are transferred to the aerial wires from which part of their energy is radiated in the
form of continuous waves.
It is found that enclosing the arc gap in an airtight chamber and feeding it with hydrogen
gas, alcoholic vapors or even steam tends to increase the potential difference as well as to
prevent the arc blowing out. It has been determined further that powerful electromagnets
mounted at a right angle to the arc, tend to increase the potential difference and, at the
same time, cause the arc electrodes to burn more evenly. For continuous operation, and
to prevent overheating, the containing chamber and the arc electrodes must be cooled by
water circulation.
In the latest naval installations, the arc gap is connected directly in series
with the antenna circuit as shown in Fig. 279, which is a duplicate of the con-
nections of the U. S. Naval Station at Radio, Va., and other naval stations. It
is claimed that con-
Y< MO VOLT5 f j^> necting the arc in this
DC. L__aX^ i» way has mcreased the
j range of such trans-
f mitters to a remark-
( "| KEY able degree, and that
- the operation of the
system as a whole has
been simplified.
Referring to the dia-
gram (Fig. 279) : The
choking inductances are
indicated at C-l and C-2 ;
the regulating resistance
for the arc shown at R
is connected in series
with the blow-out mag-
nets placed at right angles
to the arc. A source of
direct current of 500
volts is connected to the
arc gap, the plus pole of
which is constructed of
copper, the minus pole of
carbon.
An arc transmitter of
this type is adjusted for
operation as follows :
The arc is struck at low
voltage by connecting
large values of resist-
ance in the circuit at R.
The gap is then length-
ened out and the voltage
increased until the aerial
' reading.* /* is
noted that a critical
length of arc gap gives the maximum value of antenna current and this is the adjustment
always to be aimed for.
The condenser shunted across the arc (Fig. 279) acts as a by-pass for the radio-frequent
currents flowing in the antenna circuit.
Fig. 280-Details and Connections
Akxanderson Radio Frequency
TRANSMITTERS OF UNDAMPED OSCILLATIONS.
267
215. Signalling with the Arc Transmitter. — It is obvious that a telegraph
key cannot be placed in series with the arc gap for signalling and, in consequence,
the formation of the Morse characters is usually effected by changing the in-
ductance of the antenna circuit at coil L-l, Fig. 279. When the lever of the key
K is released, the radiated wave, for example, is 6,900 meters in length, but upon
pressing the key, a few additional turns of wire are inserted in the antenna circuit ;
the wave length thus is increased to 7,000 meters. Now if the receiver is tuned
to the wave radiated by the transmitter when the key is closed (7,000 meters), the
wave radiated, when the key is open (or when the key lever is up), will not be
heard in the receiving telephone, hence the Morse characters are formed at
the sender and easily distinguished at the receiver.
The wave radiated when the key is released is termed the "compensation" wave, but the
second wave is termed the "signalling zvave." In stations employing this system of signalling,
it is difficult to distinguish the signals of the sending wave unless very careful resonant
adjustments are made at the receiver, otherwise a mixture of the two radiated waves is
obtained, which cannot be deciphered.
An important feature of the arc system is the ease by which the length of the radiated
100,000 CYCLE ALTERNATOR
SPEED 20,000 R.RM.
DIRECT CURRENT MOTOR
1IOV.OLT 2000 R.F.M.
Fig. 280a— The 2 K. W. 100,000 Cycle Alexanderson Alternator.
wave can be changed. This can be instantly effected by simply adding or subtracting turns
at the aerial tuning inductance.
Undamped wave transmitters of the arc type operate most efficiently at wave lengths in
excess of 3,000 meters, and, in fact, the majority of arc stations operate at wave lengths in
excess of 6,000 meters. Satisfactory tests have been carried out between the Darien
Isthmus of Panama and San Diego, Cal., naval stations with arc sets at the wave length of
18,000 meters.
Arc generators of 100 kilowatts capacity are in daily use. The radio station at Tucker-
ton, New Jersey, under U. S. Navy control, employs a TOO K. W. arc set which, at the wave
length of 7,400 meters, gives antenna current of 150 amperes. Communication is effected
with the corresponding station at Hanover, Germany, during the favorable hours of the day.
The U. S. Naval Station at San Diego, Cal., is fitted with a 200 K. W. arc transmitter
giving an antenna current of 120 amperes; other naval stations are fitted with 30 K. W.
and 60 K. W. transmitters. The naval station under construction at Cavite, Philippine
Islands, will be fitted with a 350 kilowatt arc set giving an antenna current of 200 amperes.
Daylight communication between Radio, Va., and Darien Isthmus of Panama, and San
Diego, Calif., has been carried on for a number of months.
268
PRACTICAL WIRELESS TELEGRAPHY.
Certain battleships in the U. S. navy are fitted with 20 or 30 kilowatts arc transmitters
operating at the wave length of 4,000 meters. These sets can intercommunicate over dis-
tances of 2,000 miles in daylight.
216. The Alexanderson High Frequency Alternator. — A 2 K. W. alter-
nator (Fig. 280-a) has been developed by the General Electric Company which
generates current at a frequency of 100,000 cycles per second, the rotor of the
alternator being driven at a speed of 20,000 R. P. M. In this particular type of
generator both the armature and field windings are stationary, the rotor consist-
ing merely of a steel toothed disc. Current at 15 amperes and 130 volts is
obtained from the 2 K. W. machine, which may flow directly into the antenna
circuit or may be induced therein by an oscillation transformer. In the inductive
method, shown in Fig. 280, currents of radio-frequency flow through the primary
winding of the oscillation transformer P, the secondary S being connected in
series with the antenna. Signalling is accomplished by placing a telegraph key
in series with the field winding of the alternator or by variation of the localized
inductance in the antenna circuit, as with the arc system.
In the diagram, Fig. 280, the excitation
field winding, F, consists of a single coil,
wound inside the frame of the entire ma-
chine. The rotor is a toothed disc with
300 projections, the space between teeth
being filled with a non-magnetic material
to cut down wind friction.
The armature coils, R, R, consist each of
a single turn of wire wound zigzag in
slots, and any consecutive pair may be said
to constitute a pair of coils of one turn
each.
Current is induced in the armature coils
as follows: When a tooth on the rotor
comes opposite the armature cores, A, B,
the magnetic flux passes through windings
R, R, but a minimum of flux threads
through the coils, when the tooth lies be-
tween two armature coils. Thus an oscil-
latory current is induced in R, R, the fre-
quency of which is determined by the speed
G E. CONTROL
COILS
Fig. 281 — Showing the Fundamental Circuit of a
Radio-Frequency Control Device Developed by
the General Electric Company.
of the rotor and the number of field poles.
A unique method for controlling the antenna current of an undamped transmitter has
been developed by the engineers of the General Electric Company, the fundamental prin-
ciple of which is shown in Fig. 281. In this system, a specially constructed, magnetically
saturated, amplifying coil is connected in shunt to the radio-frequency alternator, and if a
telegraph key is inserted in the direct current circuit as at K and proper adjustment made
of the circuit connected to battery B, the effect of opening and closing the key is as
follows :
When the telegraph key, K, is up (the contacts at the rear of the lever closed), the
iron core, by proper selection of ampere turns of the coil M-2, becomes magnetically satu-
rated, and the self-inductance of the winding M-l is practically that of a 'simple coil without
an iron core. When the telegraph key is pressed and the control circuit of battery B opened,
the iron core, in respect to the winding M-l becomes magnetic, and its self-induction is at a
maximum. In this position of the telegraph key, the voltage across the terminals of the
radio-frequency alternator is maximum and maximum current flows in the antenna circuit.
In this way the dots and dashes of the Morse telegraph code can be readily formed, and
in fact, the signals may be transmitted at an extremely high speed with a practically non-
arcing control.
Practically no current is induced in the winding M-2 (the control winding) because
it includes both legs of the core of winding M-l. It is necessary in this system that the
ampere turns of windings M-l and M-2 be practically equal.
'Alternate arrangements of this circuit are in use, which are fully described in the April, 1916,
Proceedings of the Institute of Radio Engineers.
TRANSMITTERS OF UNDAMPED OSCILLATIONS.
269
270
PRACTICAL WIRELESS TELEGRAPHY.
For the transmission of speech, a microphone transmitter may be connected in the circuit
of B and wireless telephony carried on at large powers.
A photograph of a 75 K. W. high frequency alternator of the Alexanderson type appears
in Fig. 282. So far, alternators of this capacity have been used for laboratory experiments
only, but there is no reason to believe that they will not prove a commercial success, at least
at high power land stations.
Radio-frequency alternators for the production of lower frequencies, in the region of
30,000 cycles per second, are less difficult to construct than the type just described, on ac-
count of the reduced
peripheral speed of the
armature. An alterna-
tor, for example, gen-
erating current at a fre-
quency of 30,000 cycles
per second would excite
an aerial having a natur-
Lj al wave length of 10,000
meters and provided the
proper output could be
obtained would be of
great use for land station
work, but an alternator
having a normal speed of
20,000 revolutions per
minute obviously is not
practical for continuous
service at either ship or
shore stations where a
twenty-four-hour oper-
ating schedule is in ef-
fect. It is just, however,
to state that high speed
alternators such as the
Alexanderson type are
monuments of engineer-
ing skill, and many me-
chanical and electrical
vvvvW
— problems, heretofore
R considered impossible of
Fig. 283 — Complete Circuit of the Goldschmidt Alternator. solution, have been com-
pletely solved.
217. Goldschmidt Radio-frequency Alternator. — By adopting the simple
principles of electrical resonance, Dr. Goldschmidt has designed an alternator
which, by the use of a single armature, generates radio current at frequencies
from 30,000 to 75,000 cycles per second. The great advantage of this alternator
is the low speed of the armature, which, even in the 200 K. W. sizes, does not
exceed 3,100 R. P. M.
It will be observed from diagram, Fig. 280, that in addition to the stator and
rotor windings of the usual alternator, a number of external inductance coils
and condensers are connected in both the shunt and rotor circuits, which are
employed for tuning these circuits to several frequencies. In fact, by correctly
proportioning the. inductance and capacity, current at a frequency of 60,000
cycles per second can be taken from the field winding, and if made to flow in a
properly tuned antenna circuit will radiate waves, 5,000 meters in length.
In the diagram, Fig. 283, the field windings of the alternator are represented at* F (gen-
erally referred to as the stator) and the armature winding at A known as the rotor. The
armature inductance A and the condenser C-4 are shunted by the inductance L-3 and the
condenser C-5. Similarly, L-3 and C-4 are shunted by condenser C-3. The values of C-4,
L-3, C-5 and A are so chosen that either C-4 and A, or C-5 and L-3 are in resonance to the
initial frequency of the generator, that is to say, C-4 and A or C-5 and L-3 have identical
TRANSMITTERS OF UNDAMPED OSCILLATIONS. 271
time periods and since they are connected in parallel, the period of the circuit remains
unchanged and in resonance with the initial frequency of the alternator. The function of
inductance L-3 and condenser C-4 is to place the armature on short-circuit at a given
frequency. In fact, it would not be possible to completely short-circuit the rotor winding
for radio-frequent currents by merely placing a short piece of wire across the terminals.
However, by placing another circuit containing inductance and capacity of identical time
period in shunt to the rotor, a complete short-circuit is effected.
The circuit of the stator F, C-l, L-2 and C-2, are similar to those of the rotor A, but this
circuit is tuned to twice the fundamental frequency of the alternator. Also, the distributed
capacity of the antenna system takes the place of the condenser, C-3, of the rotor circuit.
The field winding of the stator, F, primarily magnetized by the source of direct current,
B, has the choking coil, L-l, connected in series to prevent the oscillations of radio-frequency
flowing back to the exciter B. A regulating rheostat R permits close variation of the field
current.
It will assist the student to gain an understanding of the operation of this generator, if
he will but consider the following well-known phenomenon : If a common alternating cur-
rent generator armature revolves at such speed as to generate an initial current at a fre-
quency of 60 cycles per second, and the field coils, for example, are mechanically rotated in
the opposite direction at a similar speed, it is plain that the relative motion is doubled and
therefore the frequency will be doubled. It is also established that we might dispense with
the revolving appliances for the field coils, and pass an alternating current of a given
frequency through a stationary field winding.
If the speed of the armature is N1 revolutions per second and the frequency of the field
current N cycles per second, there will be induced in the armature E. M. F.'s of two fre-
quencies, one of N -f- N1, and another of N — N1.
In case N and N1 are just equal, then, the frequency of the current induced in the arma-
ture will be N -j- N1 or 2N, and N — N1 or zero. Hence, if current of 60 cycles flows
through a four pole field winding and the armature is driven at 30 revolutions per second,
current at a frequency of 120 cycles per second will be generated in the armature.
The student, having some knowledge of the fundamental principles of the induction
motor, is well familiar with the fact that a rotating magnetic field is produced by an alter-
nating current flowing through a stationary field winding. Such a current flowing through
the stator of a generator, for instance, will give rise to two oppositely rotating magnetic
fields of angular velocity corresponding to the frequency of the current, and if the speed
of the armature is carefully adjusted to the velocity of the field, it will cut through one of
these fields and thereby double the frequency, but it will be stationary in respect to the other
field.
By employing several generators to step-up the frequency, this principle might be ex-
tended further. For instance, current of a certain frequency generated in the armature of
generator No. 1 could be passed through the field winding of generator No. 2 and by proper
selection of armature speeds, the frequency would be doubled in the second generator,
and so on. But, owing to the number of steps involved in such frequency transformation,
there would be serious current losses which could not be compensated for. However, Gold-
schmidt's alternator accomplishes this in a single armature and by adoption of the principles
of electrical resonance, several frequencies are generated in the armature and field windings.
The current of one of these frequencies is selected and diverted to the antenna system where
part of the energy is radiated in the form of electromagnetic waves.
The design of Goldschmidt's alternator is such that when driven at normal speed, the
initial frequency of the current generated in rotor A is 15,000 cycles per second. Since the
inductance and capacity of the rotor circuit are selected to give it a natural time period of
oscillation suitable to the fundamental frequency, an alternating current of considerable
intensity flows (in the armature windings A, C-4, L-3, C-5).
The field of the rotor corresponding to this frequency is composed of two component
magnetic fields of equal intensity, which rotate in opposite directions in respect to the wind-
ings of the rotor. The velocity of one of these fields is zero in respect to the rotor, but the
other travels at twice synchronous speed and therefore induces in the circuits of the stator
an E. M. F. at a frequency of 30,000 cycles per second (and zero frequency) (N -f N and
N — N or 2N and 0). And since the circuit F, C-l, L-2 and C-2 is tuned to this frequency,
current of considerable amplitude flows.
Now the E. M. F. of 30,000 cycles, induced in the stator, induces in the rotor two fre-
quencies, one of 45,000 cycles per second and another of 15,000 cycles (2n -f N and 2N — N
272
PRACTICAL WIRELESS TELEGRAPHY.
or 3N and N). The current of 45,000 cycles flows through the condenser C-3, but the
current of 15,000 cycles can, by proper design of the circuits, be made to nearly neutralize
the former current of 15,000 cycles in the rotor. There remains, therefore, in the rotor, an
E. M. F. at a frequency of 45,000 cycles per second which flows through the condenser C-3,
and due to a well-defined resonant adjustment, a powerful current flows.
DIRECTION OF
CURRENT i CYCLED
n= 10,000
Fig. 284— The Joly-Arco Undamped Wave Transmitter.
The current of 45,000 cycles flowing in the rotor, will induce in the winding of the stator,
current at 30,000 cycles per second and 60,000 cycles (3N — N and 3N -f- N or 2N and 4N).
This -current of 30,000 cycles nearly neutralizes the former current of 30,000 cycles, leaving
in the circuits of the stator, current at a frequency of 60,000 cycles, to which the antenna is
carefully tuned. Because the impedance of L-2, C-2, is considerably greater than that of
the antenna, the current of 4N oscillates in the antenna circuit.
Signalling is accomplished in the Goldschmidt system by placing a key in the exciter cir-
cuits, the circuit being alternately opened and closed.
An alternator of this type installed at the radio station, Tuckerton, New Jersey, U. S. A.,
is employed for transatlantic communication with a corresponding station located at Han-
TRANSMITTERS OF UNDAMPED OSCILLATIONS. 273
over, Germany. Although capable of generating 200 K. W.. it is'normally used at 100 to 150
K. W. The driving motor is of 250 H. P. capacity, operated from 220 volts direct current
and has a speed of 4,000 R. P. M.
The armature of the generator is constructed of very thin laminated iron and revolves
within 1-32 of an inch from the field poles. Oil is pumped to the bearings at considerable
pressure and afterwards cooled through a refrigerating machine.
Operated at the wave length of 7,400 meters with a generator input of 175 K. W., 135
amperes flow into the antenna at the Tuckerton station. When atmospheric electricity is
not severe, communication is maintained with Hanover, Germany, but the stations operate at
a disadvantage because they are not duplexed as are the Marconi Transoceanic stations.
218. The Joly System for the Production of Undamped Oscillations. — The
U. S. Radio station at Sayville, Long Island, employs the Joly-Arco system for the produc-
tion of continuous waves. In this system a specially designed generator having an initial
frequency of 10,000 or 15,000 cycles per second is connected to two transformers having
magnetically saturated iron cores which are designed to double or triple the frequency of
the alternator.
A fundamental circuit diagram of this system is shown in Fig. 284, wherein an alternator
N having an initial frequency of 15,000 cycles per second is connected to the two specially
designed transformers, T and T-l. Transformer T has the excitation winding S, which
saturates the core fully, a similar winding S-l being provided for the transformer T-l.
A source of direct current for the excitation windings S and S-l is indicated at B with
the regulating rheostat, R, connected in series. The current generated by the alternator N
flows through the primary windings C and A, the complete primary circuit being tuned to
resonance with the initial frequency of the alternator by the variable inductance and the
variable condenser connected in series with the circuit.
The secondary circuit, or antenna system, embraces the windings D and B connected in
series with the antenna inductance L, the earth connection E and the aerial wires W. The
hot wire ammeter M is connected in series with the earth lead to determine conditions of
resonance. As intimated previously, the transformers T and T-l are fully saturated, the
magnetization being brought to the knee or bend of the characteristic saturation curve by
carefully regulating the rheostat R.
To illustrate the functioning of this apparatus, let us assume that the primary coils are
wound on the cores so that the direction of the magnetic lines of force will be that indicated
by the full-line arrows; furthermore, assume that at a particular half cycle of current from
the alternator, the direction of the current through the primary winding is such that the
corresponding magnetic flux flows in the direction indicated by the broken-line arrows ; then
the normal flux of the core T will not be increased because this core is already saturated
fully, the added flux flowing in the direction of the core flux, but the normal flux of the
core T-l will be opposed by the flux of the winding A and the total lines of force flowing
through the core, therefore, reduced. This reduction of flux, followed by subsequent rise
to normal saturation upon the completion cf an alternation from N, causes two changes of
flux through coil B of transformer T-l, resulting in the production of two alternations in
that winding for one alternation of current from N. The final effect is to induce current of
double frequency in the antenna system.
Let the next half cycle of the alternator N be completed through windings A and C ;
then, the change of flux takes place in the core of the transformer T, rather than in T-l,
resulting in the induction of two alternations of current in the secondary winding D. Sum-
ming up the foregoing, a complete cycle of current from the generator N will induce two
alternations of current in the coil B, followed by two alternations of current in the coil D,
thereby doubling the initial frequency of the generator current. This current flows in the
antenna circuit which has been carefully tuned to resonance, and part of the energy is con-
verted into electric waves.
By an additional set of transformers, the current of double frequency generated by the
first set of the transformers may be again doubled, but the efficiency of the apparatus, as a
whole, decreases considerably as the steps of transformation are increased.
Another system of transformation has been evolved by Joly, in which the frequency ot
the generator may be tripled by a single set of transformers, which are adjusted to have —
when A. C. current flows — unequal degrees of saturation. In this system the D. C. excita-
tion winding for the transformer is dispensed with.
In systems of this type in order that resonance between the alternator current
and the antenna system may be maintained, it becomes important that the fre-
274
PRACTICAL WIRELESS TELEGRAPHY.
quency of the alternator may remain constant ; in consequence, the speed of the
driving motor must be carefully governed and to this end several devices have
been brought forth, the principal one being a signalling key fitted with a special
set of contacts which, just previous to the closing of the key, add resistance in
the motor field circuit, maintaining a practically uniform speed of rotation.
Fig. 285 — Marconi's Method of Generating Continuous Oscillations.
Signalling is accomplished, in the Joly system, by inserting a key in series with the direct
current excitation winding, or by interrupting the generator circuit to the primary winding
of the transformers by a special electromagnetic key, or by cutting in and out a few turns
of the aerial tuning inductance. The first-named method is the one in use at present. The
alternator at the Sayville station has a capacity of 100 kilowatts and gives antenna current
of about 140 amperes. Fair communication is effected with the station at Nauen, Germany,
throughout the 24 hours of the day, but the best results have been obtained during the dark
hours. At present the Sayville station operates at the wave length of 9,400 meters, the
antenna frequency being slightly above 30,000 cycles per second.
219. Marconi's System for the Production of Continuous Waves. — Signer
Marconi and his engineering staff have developed an ex-
ceedingly novel method for generating continuous oscilla-
tions, doing away with many of the problems encountered
in the construction of intricate High frequency alternators.
The fundamental principle upon which the system is based is
disclosed in the diagram, Fig. 285, wherein a number of disc dis-
chargers, D-l, D-2, D-3, D-4, are mounted on a common shaft,
each of which is connected to an oscillation circuit, such as P-l
and C-l, P-2 and C-2, etc. The main condensers, C-l, C-2, C-3,
C-4, are charged by a source of high potential direct current, indi-
cated at G, consisting of two 5,000 volt generators connected in
series. The disc dischargers, D-l, D-2, etc., are set on the shaft so
that the condensers discharge and recharge at regular intervals in
succession, and if the velocity of the discs is adjusted so that the
interval between the beginning of the discharge of one condenser
and the beginning of the discharge of the next condenser is equal
to the period of the oscillations in the antenna circuit, or an exact
multiple thereof, the oscillations flowing in the antenna circuit will
overlap, producing continuous oscillations of practically constant
amplitude, as shown in Fig. 286.
To insure that each condenser discharges at the right moment,
and that the successive groups of oscillations induced in the antenna
circuit are in phase, the discharge circuit is provided with an auxiliary timing rotary disc
discharger, known as the trigger or timing disc (not shown in the drawing), which performs
the function of setting off the main spark discharge at the proper time.
Fig. 286— Showing How
Groups of Damped Oscil-
lations Can Be Made to
Overlap One Another.
TRANSMITTERS OF UNDAMPED OSCILLATIONS.
275
A modified form of the timed-spark oscillation generator is shown in U. S. Patent 1,136,477
of 1915, one arrangement being that shown in Fig. 287. Here a direct current generator is
indicated at G and a choking coil at L-l. Since G has an electromotive force of about 10,000
volts, condensers K-l and K-2 receive a charge which enables them to discharge across the
spark gap. A terminal of either condenser is connected to the disc dischargers, D-l and D-2,
and the studs of the latter are placed so that condensers C-l, C-2 and C-3 are alternately
and successively charged, let us say, through inductance L-2 and successively discharged
and recharged through L-3.
The oscillations set up in L-2 or L-3 are made to act inductively on an intermediate
circuit, L-4, L-5 and C-4, and if the discs be revolved at a certain speed and are properly
timed, the trains of oscillations induced in the intermediate circut overlap one another, re-
sulting in a continuous flow of oscillations in the antenna circuit, A-l, E.
Fig. 287 — One Type of Marconi Continuous Wave Generator.
In ths system, signalling is accomplished by inserting a high tension relay key in series
with the source of direct current from the generator or by closing the circuit of the timing
disc.
The apparatus for this system has been developed further by the Marconi's Wireless
Telegraph Company, Ltd., and is not used at present as shown in either Figs. 285, 286 or 287.
The details of the more modern apparatus cannot be published for the present, but it may
be remarked that a transmitting set of this type is in daily use at the great Marconi station
at Carnarvon, Wales, England, and a similar set will be installed in the transoceanic station
at Marion, Mass., U. S. A.
With a power input of less than 100 K. W., the author has copied the signals from the
Carnarvon station in New York City during the daylight hours with an aerial 100 feet in
length. The signals were considerably stronger than those obtained from other foreign
276
PRACTICAL WIRELESS TELEGRAPHY.
stations using radio-frequency alternators of greater power. The wave length employed
during these tests was close to 10,000 meters.
220. The Pliotron Oscillator. — Highly exhausted two or three element
vacuum valves of enlarged dimensions can be employed to generate current at audio- or radio-
frequencies. In the form designed by the engineers of the General Electric Company, the
device has been termed a "Pliotron." The Pliotron bulb contains a tungsten filament F (hot
cathode) brought to a state of incandescence by 110 or 220 volts direct current, a grid of
tungsten, G, and a tungsten plate, P, (anode), as indicated in Fig. 288.
The filament F is brought to incandescence by a source of 110 volts direct current, A, B,
which source also supplies current for the anode circuit between the filament and the plate.
The radio-frequency inductance of the anode circuit, indicated at L, is shunted by the
condenser C-l. L-2, the radio-frequency inductance of the grid circuit, also has the shunt
condenser C-2. By variation of the capacity of C-l and C-2, the grid circuit and anode
circuit may be tuned to resonance and the oscillations flowing in the anode circuit repeated
back to and reinforced through the grid circuit by inductively coupling coil L-l to L-2.
By means of a third winding, L-3, coupled to either L-l or L-2, current of any desired
frequency can be gen-
erated by proper varia-
tion of inductance and
capacity ; in fact, cur-
rent at frequencies from
60 to 1,000,000 cycles
per second can be ob-
tained.
The radio-frequent
currents generated in
the circuits of the
Pliotron can be trans-
ferred to the antenna
system by connecting
the terminals of the
coil L-3 to the antenna
and earth wire, the
precaution being taken
to tune the aerial cir-
cuit to resonance with
the local current. A
number of Pliotrons
may be connected in
parallel and direct cur-
rent at any desired
power converted into
^^^ oscillations of radio-
^ST frequency.
The Pliotron vacuum
Fig. 288 — The Pliotron Oscillator Connected for the Production of Radio- bulb Can also be Used to
Frequency Oscillations. yary ^ ampljtude of
the oscillations in an antenna system traversed by undamped oscillations. If properly con-
nected, it is applicable for radio-telephony as well as telegraphy. If the anode of the Pliotron
is connected to a point of high potential in the antenna system and the negative side of
the filament to earth, and the grid potential of the Pliotron is strongly negative, no leakage
to earth takes place, but if the negative potential is decreased, sufficient energy will be with-
drawn from the antenna to strongly damp the oscillations. In fact, practically all the energy
of the antenna oscillations can thus be diverted to earth.
If an electromotive force of the correct value is impressed upon the grid through a
small telegraph key, the dots and dashes of the Morse code are formed by simply closing
the circuit and thus varying the grid potential.
PART XV.
RECEIVERS FOR UNDAMPED OSCILLA
TIONS OR CONTINUOUS WAVES.
221. THE PROBLEM. 222. THE TIKKER. 223. THE HETERO-
DYNE SYSTEM. 224. THE VACUUM VALVE AS A SOURCE OF
RADIO-FREQUENCY OSCILLATIONS. 225. VACUUM VALVE AS A
COMBINED DETECTOR, AMPLIFIER AND BEAT RECEIVER. 226.
OSCILLATING VACUUM VALVE DETECTOR CIRCUITS OF THE U. S.
NAVY. 227. THE GOLDSCHMIDT TONE WHEEL. 228. MARCONI
SYSTEM FOR RECEPTION OF UNDAMPED OSCILLATIONS.
(4)
221. The Problem. — If an ordinary crystal rectifier be connected to a
receiving set tuned to a continuous wave transmitter, owing to the lack of discon-
tinuity in the advancing wave, a continuous pulsating current flows through the
receiving telephone. These pulsations take place at such rapid rates that the
diaphragm of the telephone is either held down continuously or repelled continu-
ously resulting in no sound except at the beginning or end of the flow.
To make undamped oscillations audible, we are compelled to break up the
oscillations of either the transmitter or receiver into groups suitable for maximum
response in the head telephone or to supply other means at the receiver to make
them audible.
The receivers at present in use are :
(1) The Poulsen tikker or chopper;
(2) The "Heterodyne" system;
(3) The Goldschmidt Tone Wheel;
The Regenerative Vacuum Valve (used as a "beat" receiver).
The mode of func-
tioning of these detectors
is briefly described as
follows : The Poulsen
tikker interrupts the cir-
cuits of the receiving
tuner at a uniform rate
per second (approxi-
mately 300 to 600 times} ;
the heterodyne system is
based upon the interac-
tion of two radio-fre-
quent currents in the
receiving aerial, resulting
in the production of an
audio-frequent current in
the telephone circuit; the
Goldschmidt tone wheel
converts the current of
radio-frequency (the in-
PHONES coming oscillations) into
an audio-frequent current
and the regenerative
Fig. 289— The Simple Poulsen Tikker and Circuit. "beat" receiver employs
278
PRACTICAL WIRELESS TELEGRAPHY.
the vacuum valve as an oscillator at radio-frequencies to produce the "heterodyne" effect.
This, combined with the well-known relaying action of the vacuum valve and its ability to
repeat currents of radio-frequency, makes a receiver of unusual sensitiveness.
222. The Tikker. — In its commercial form the tikker consists of a com-
mutator interrupter, the principal of which is shown in Fig. 289.
A disc D mounted on the shaft of the motor M has a number of teeth filled in between
with insulating material such as fibre. The radio-frequent currents flow from brush B to A
through the disc which interrupts them from 300 to 1,000 times per second. The charge built
up in the condenser, C-l, by resonance with the aerial system discharges into the telephone
condenser, C-2 (Fig. 289), at regular intervals. Condenser C-2, in turn, discharges through
the head telephone creating a single sound for the charge accumulated. Due to the fact
that the tikker discharges C-l at various potentials, or we might say, at different points on
the cycle of the incoming oscillations, a non-uniform note is produced lacking the desired
musical pitch for reading through atmospheric electricity. However, the tikker suffices as a
simple receiver and good results have been obtained by its use at several ship and shore
stations.
A favored form of circuit interrupter for the reception of undamped oscillations is the
sliding -ivire or slipping contact detector, shown in Fig. 290. In the diagram a small brass
wheel, W, mounted on the shaft of the motor, M, is in contact with the brush B. The
terminals of the slipping contact, B, are connected in the circuit of the tuner as the tikker,
D, of Fig. 289. The cir-
B mmm _ cuit is completed
through the brush, B-l,
in contact with the shaft
S. When the wheel is
in rotation, there is a
constant slipping and
gripping of the brush B
on the wheel which
makes a contact of vari-
able resistance, causing
the charge accumulated
in the telephone con-
denser to vary in ac-
cordance. The note in
the telephone will have
a pitch in accordance.
Both the tikker and
the slipping contact de-
tectors are considered
as "current operated" devices, meaning that they function best in a tuning circuit which
affords a maximum of current rather than a high voltage. The coils of the tuner for these
oscillation detectors are wound with Litzendraht wire or conductors of equal high frequency
conductivity.
These detectors are applicable to the reception of damped oscillations or discontinuous
waves, but, owing to the discontinuity of the wave trains, an irregular note, much similar
to the discharges produced by atmospheric electricity, is obtained.
223. The Heterodyne System. — The functioning of the heterodyne* re-
ceiver is based upon the interaction of alternating currents of two frequencies in
some part of the receiver circuits.
For example, if an alternating current of 50,000 cycles per second flows through a given
circuit, and there is superposed on it another current having frequency of 49,000 cycles per
second, a "beat" current will result having a frequency equal to the numerical difference
of the two applied frequencies or 1,000 cycles per second. The same frequency would be
obtained by superposing a current of 51,000 cycles upon another current of 50,000 cycles; in
fact, in any case, the frequency of the beat current could be the difference of the two
applied frequencies.
By adoption of this principle we are afforded ready means for making audible undamped
oscillations from a given transmitter at the receiver. One method is shown in Fig. 291,
Fig. 290— The "Slipping Contact" Detector for Reception of Undamped
Oscillations.
* Abroad, this receiver is called the "local interference" receiver.
JL D
RECEIVERS FOR UNDAMPED OSCILLATIONS PR WAVES, i 279
where the receiver circuits are indicated by L-l, L-2, the crystal rectifier D, etc. An un-
damped oscillation generator consisting of the D. C. arc gap A, B, the variable condenser C
and inductance L are shown at the base of the drawing/ By means of this generator, a steady
stream of oscillations is supplied to the aerial system through the coupling coil L-3, the
frequency of which can be altered either
by the condenser C or by the induct-
ance L.
Now, if the receiving tuner, for ex-
ample, is tuned to the wave length of
6,000 meters corresponding to an oscilla-
tion frequency of 50,000 cycles per second
(which may be the wave length of a given
transmitting station), and the arc genera-
tor adjusted to generate oscillations at a
frequency of 49,500 cycles per second, a
beat current of a frequency of 500 cycles
per second will flow in the circuit of the
receiver where it will be rectified by the
detector, D, and made audible in the head
telephone P.
By carefully adjusting the local fre-
quency, the beat note can be varied from
a pitch equivalent to that of a 200 cycle
alternating current up to the limits of
and beyond audibility. The interaction of
these two frequencies in the receiving
system not only makes undamped oscilla-
tions audible but also amplifies the re-
ceived signal to a marked degree. Even
damped oscillations may be amplified by
this means, but in this case the normal
note of the spark transmitter is distorted,
UNDAMPED OSCILLATION
GENERATOR
MO VOLTS O.C.
Fig. 291 — Early Form of Heterodyne Receiver.
the resultant note being of lower pitch. The note of the local beat current generated by the
heterodyne receiver has the most uniform pitch when the sending station employs a radio-
frequency alternator; although flute-
OSCILLATIONS ^e tones are obtained from arc trans-
mitters, the "beat" current does not
have anywhere near the musical pitch
that can be obtained from the radio-
frequency alternator. The arc gener-
ator of Fig. 291 might be replaced by
a radio-frequency alternator of small
output or by a buzzer excitation sys-
tem, but a generator giving genuinely
undamped oscillations is preferred.
The precise actions taking place in
the heterodyne receiver of Fig. 291 can
be explained by the series of curves in
Fig. 292. The oscillations O-l, indi-
cated on the upper line, are those in-
coming at a given station (without the
local arc generator in operation) while
those on the second O-2 correspond to
the frequency of the arc generator and
are of a lower order of frequency than
the incoming oscillations.
The third curve O-3 indicates the
resultant "beat" current due to the in-
teraction of the local frequency and
that of the incoming signal. This cur-
Fig. 292-Curves Showing the Functioning of the Heterodyne rent haSr ZG™ ™1UC whe" *« ^O
Receiver. groups of oscillations oppose and max-
280
PRACTICAL WIRELESS TELEGRAPHY.
RECEIVER CIRCUIT
imum value when they assist or are in phase, and the frequency of the beat current is the
numerical difference of the frequency of the incoming oscillations and that of the local
generator.
When rectified by the crystal, the successive cycles of the beat current take the form of
the curve O-4, where the negative halves have been cut off and the positive halves remain,
for operation of the telephone, as shown by the heavy curved line O-5.
224. The Vacuum Valve as a Source of Radio-Frequency Oscillations.
— If a three element vacuum valve is connected up as in Fig. 293 with the correct values of
inductance for the coils L-4, L-5, L-6 and L-7, and for the condensers, C-3, C-4 and C-5,
oscillations of radio-frequency flow through L-4, the periodicity of which may be varied
principally by C-3 and C-5. Connected in this manner, the vacuum valve becomes a gen-
erator of sustained oscillations which may interact with the incoming oscillations for the
production of "beat" currents. For the maximum strength of signals, the coil L-4 bears a
certain critical coupling
to L-3, and the coupling
between L-5 and L-6,
V ' I / also requires care-
\ / f ul adjustment for steadi-
^* ness and constancy.
The "beat" current set
up in the receiver wind-
ings L-2 and condenser
C-2 is rectified by the
crystal rectifier D, and
made audible in the head
telephone P.
Increased strength of
signal is obtained by the
use of a single three ele-
ment vacuum valve or a
triple valve amplifier in
place of the crystal recti-
fier D.
Since the reception of
very long wave lengths
is involved in a system of
this type, the inductances
L-7 and L-8 are of the
order of 90,000 micro-
henries each. It has been
found possible to design
a beat receiver tuner hav-
ing fixed values of in-
ductance throughout, the
required changes in fre-
quency for "heterodyn-
ing" being obtained by
variable condensers.
225. Vacuum Valve as a Combined Detector, Amplifier and Beat Receiver.
— Much of the record-breaking, long distance transmission effected, of late, is due to the
vacuum valve being employed as a combined detector and "beat" receiver. One circuit of
this type is shown in Fig. 294, wherein it will be observed that the secondary circuit, L-4,
L-3, C-2 and L-5, can be placed in resonance with the tertiary circuit, L-6, L-7 and C-4,
and when the filament is brought to the correct degree of incandescence by the rheostat R,
the discharge of condenser C-4 through L-7 and L-6 starts the flow of undamped oscilla-
tions which are transferred to the secondary circuit through L-5 and L-6.
Due to the relaying action of the valve, the oscillations are repeated back to the grid
(of the valve) and accordingly amplified.
Now if the antenna circuit, L-l, L-8 and L-2, is adjusted to the frequency of the incom-
ing oscillations, and the secondary, as well as the tertiary circuit; adjusted to a slightly
VACUUM VALVE GENERATOR
Fig. 293 — The Vacuum Valve Heterodyne Receiver.
RECEIVERS FOR UNDAMPED OSCILLATIONS OR WAVES.
281
different frequency of oscillation, a beat current is set up in the secondary circuit, which is
amplified in the local telephone circuit by the charge placed upon the grid.
As explained by Armstrong, the incoming oscillations are transferred from the antenna
circuit to the secondary circuit in the usual manner, and due to the repeating action of the
valve, they are reproduced in the tertiary circuit, coupled back to the secondary circuit
through the coupling transformer, L-5 and L-6. and re-enforced, all this taking place while
the valve is generating oscillations locally. Simultaneously, beats are produced by the
interaction of the local oscillations and the incoming oscillations, the effect being to alter-
nately increase and decrease the amplitude of the oscillations in the complete system.
\/
'BEAT' RECEIVER FOR DAMPED AND UNDAMPED
OSCILLATIONS.
L-a
Fig. 72
Fig. 294 — Complete Circuits of a Beat "Receiver.
An increase in the amplitude of the grid oscillations, increases the negative charge in the
grid condenser, producing a decrease in the average value of the B-2 battery, and, therefore,
a decrease in the telephone current, but a decrease in the amplitude of the local oscillations
allows some of the negative charge in the grid condenser to leak off and thereby permit an
increase of the telephone current. The result of all this is the production of an alternating
current of audio-frequency, which is practically a simple harmonic current.
(a) Operation and Adjustment. For wave lengths between 6,000 and 10,000 meters, the
tuning for the secondary and tertiary circuits is done principally at the condensers, C-2
and C-4. Also the coupling between L-5 and L-6 must be carefully adjusted for maximum
response. Careful regulation must be made of the voltage of the B-2 battery, which
normally varies from 50 to 150 volts, depending upon the type of valve in use. The vari-
ometer inductance L-8 is a useful element of the antenna system for variation of its natural
282 PRACTICAL WIRELESS TELEGRAPHY.
frequency. It affords a close adjustment of inductance between the taps of the multi-point
switch, and also permits variation of the frequency of the beat current.
It facilitates the preliminary adjustment of this receiver if access can be obtained to an
accurate wave-meter. The wave-meter, shunted by a buzzer excitation circuit, is placed in
inductive relation to the earth lead of the antenna system, and the signals at any particular
wave length of the wave-meter are recorded on the receiving apparatus. In this manner a
precalibration is effected, eliminating all guesswork. It is not difficult, however, to tune the
apparatus to an undamped transmitter without a wave-meter, if certain precautions are
observed. To begin with, the coil L-5 is placed in slight inductive relation to L-6. L-4 is
placed about half way inside L-2 and the coil L-7, generally, is used at its maximum value.
The condenser, C-3, is used at an exceedingly small value of capacity (very near to zero).
The condensers, C-2 and C-4, are varied simultaneously in capacity until a peculiar "thump-
ing" sound is heard in the head telephone. Near to this point the secondary and local
telephone circuit are in oscillation and in resonance.
It is found that the vacuum valve having less than the maximum amount of exhaustion,
oscillates far below the characteristic "blue glow" point. On the other hand, this glow is not
evident, in the highly exhausted valves, regardless of the locally applied voltage. The
correct adjustments throughout, in this type, are determined by experiment.
We may resume the complete process of tuning a receiving set of this type as follows:
The antenna system is tuned to resonance with the incoming wave, but the secondary and
tertiary circuits are set into oscillation at a slightly different frequency. Due to the inter-
action of the two currents, "beat currents" within the limits of audibility are produced and
by variation of the local frequency, the pitch of the note in the head telephone may be varied
over a considerable range. In manipulating this apparatus it is shown, during the reception
of undamped oscillations, that proper adjustment has been attained when, if the variable
elements (the coils and condensers) of either of the associated circuits of the complete
tuner are altered in value, the pitch of the note changes accordingly. During the initial
adjustment, and afterward the body of the manipulator must be kept at a considerable
distance from the high potential ends of the tuning coils, otherwise the circuits will be
thrown out of resonance and the signals will disappear.
With the apparatus of the foregoing type, signals have been received in New York City
from a certain transmitting station at Honolulu at a distance of approximately 6,500 miles.
Dimensions of a receiving set of this type, adjustable to wave lengths up to 10,000 meters,
which has been tried and tested experimentally, follow:
Referring to the diagram, Fig. 294, the high voltage battery, B-2, consists of from 50 to
100 miniature flashlight cells adjustable in steps of three at a time or preferably singly. The
filament battery B-l generally does not exceed four volts, although valves have been con-
structed having 12 volt filaments. The rheostat R has resistance varying from 10 to 20
ohms. It is essential that it be closely adjustable.
The inductance coil of the local telephone circuit, L-7, is 26 inches in length and Sl/2
inches in diameter, wound closely with No. 28 S. S. C. wire. The coil, L-6, is 6 inches in
diameter by 6 inches in length, wound closely with No. 26 S. S. C. wire. The coil, L-5, is 6
inches in length, wound closely with No. 26 S. S. C. wire. The coil, L-5, is also 6 inches in
length by 5l/2 inches in diameter and mounted so it can be placed in variable inductive
relation with L-6. It is rarely necessary to place L-5 completely inside of L-6, but the
coupler should be constructed to permit the coupling between the two coils to be adjusted
over a fair range. The coil, L-5, is also wound with No. 26 S. S. C. wire.
The secondary winding of the receiving tuner, L-4, is 5 inches in diameter by 14 inches
in length, covered with No. 28 S. S. C. wire. The secondary loading coil, L-3, has similar
dimensions to the coil L-7, each of which may be wound on a cardboard form or hard
rubber tube.
The secondary condenser, C-2, has maximum capacity of .0005 microfarads and preferably
is constructed so that the zero position on the condenser scale actually represents zero
capacity. The grid condenser, C-3, has the same capacity as the condenser, C-2. Both
condensers should be fitted with handles at least 12 inches in length, in order that the
constants of the circuit are not changed by the body of the manipulator. The condenser,
C-4, should have a maximum capacity of .002 microfarads.
The primary winding, L:2, is Sl/2 inches in diameter by 12 inches in length, covered with
No. 24 S. S. C. wire. It is somewhat difficult to give complete dimensions for the aerial
tuning inductance, L-l, unless the inductance and the capacity of the antenna with which
it is to be employed is known, but for receiving work with an aerial having a natural period
of 450 meters, it may be 28 inches in length by 3l/2 inches in diameter, wound closely with
RECEIVERS FOR UNDAMPED OSCILLATIONS OR WAVES.
283
No. 22 S. S. C. wire. A tap-off should be taken every inch and led to the contacts of a
multiple point switch. The leads to the switch from the tap-off should not be "bunched"
but spaced as far as possible.
226. Oscillating Vacuum Valve Detector Circuits of the U. S. Navy. —
A modified vacuum valve circuit for the reception of undamped oscillations by the produc-
tion of "beats," is described by Dr. Austin in the Proceedings of the Institute of Radio
Engineers. It is a duplicate of the circuit developed at the Naval Laboratory and employed
at Naval stations throughout the United States and outlying possessions.
It will be noted from the diagram, Fig. 295, that a certain similarity exists between this
circuit and the one described in the previous paragraph, both generating a "beat" current
by the superposition of locally generated oscillations upon those of the incoming wave.
It is to be noted, first, that the two terminals of the secondary winding are connected to
the grid and plate of the vacuum valve rather than to the grid and filament, the more usual
connection; and, upon close examination, the secondary and tertiary circuits are found to
be electrostatically and electro magnetically coupled through the condenser C-5 and head
telephone P respectively. And, as in the former circuit, the incoming oscillations and the
final audio-frequent currents are reinforced by repeating them back to the grid. Simultane-
ously, by adjustment of condensers, C-5, C-l and C-2, the valve generates oscillations locally
at a frequency determined by the constants
of the secondary and tertiary circuits.
A novel feature of this circuit is the
placing of the head telephone in shunt to
the battery, B-2, rather than in series, but
it is claimed by Dr. Austin that this con-
nection results in a decrease of interference
from atmospheric electricity.
An important adjunct to this system is
the so-called "sensitizing circuit" L-4, C-3.
It is advanced by Dr. Austin that this cir-
cuit reduces the amplitude* of the local
oscillations and therefore increases the
strength of the received signals from three
to four times. It also permits looser
coupling between the primary and second-
ary circuits of the system, thus cutting
down the interference of static.
A different and more plausible explana-
tion is advanced by Armstrong for the
action of the "sensitizing" circuit. Accord-
ing to this investigator, when the grid cir-
cuit of the vacuum valve is set into oscilla-
tion at a frequency differing from the in-
coming oscillations, the reactance of the
circuit to the local oscillations is zero, but
the reactance and therefore the impedance
to the incoming oscillations is considerable
and results in a loss of energy (due to the dissimilarity of the wave length adjustment of
the primary and secondary circuits).
Now the effect of coupling the "sensitizing" circuits to the grid circuit, is to give the
latter two frequencies of oscillation differing by 1,000 to 1,500 cycles. By adjusting the system
to oscillate at one of the resulting frequencies and having the other "coincide with that of the
incoming oscillations, zero reactance is obtained and the signal strength accordingly increased.
Owing to the severe discharges of atmospheric electricity experienced at the U. S. Naval
Stations, it has been found necessary to connect the grid of the valve to earth through a
small variable condenser; for, otherwise, communication between the naval stations could
not be maintained.
No explanation of the function of the audio-frequency impedance coils, with the iron
cores, has been advanced.
It is needless to say that many other circuits, when used in connection with the
Fig. 295 — Beat Receiver Circuit as Employed at the
U. S. Naval Station.
*This is an important consideration in the operation of the heterodyne, namely, that the amplitude
of the locally generated oscillations be carefully regulated for maximum response.
284
PRACTICAL WIRELESS TELEGRAPHY.
purpose
P.ADIOFREQUENCY
TRANSFORMER
RADIO FREQUENCY
TRANSFORMER
Fig. 296 — Showing the General Electric Company's Cascade Connection of
Electron Relays.
vacuum valves, have been found suitable to the reception of undamped oscillations; in fact,
the majority of these circuits are equally well adapted for the reception of damped oscilla-
tions, but, as mentioned previously, the normal note of a spark transmitter is distorted when
the maximum amplification is obtained.
(a) G. E. Amplification Relays. One system of connecting magnifying relays for the
•pose of first increasing the amplitude of the oscillations of radio-frequency is set forth in
Fig. 296, which is a
method of connection
particularly suited to the
pliotron oscillators of the
General Electric Com-
pany.
It is to be observed
that the usual grid con-
denser is excluded from
the circuit of all valves
except the last one.
The oscillations of
radio-frequency are re-
peated from one bulb to
the other, and in the last
bulb they are made audi-
ble by being rectified,
e. g., each group of oscillations places a charge in the grid condenser which has a relaying
effect upon the battery circuit of bulb No. 3 (over the duration of a wave train), causing a
single sound for each spark of the distant transmitter.
The foregoing explains the functioning of this circuit during the reception of damped
oscillations, and it should be mentioned that this system for repeating radio-frequencies
affords a marked degree of selectivity. For example, if each of the tuned circuits is adjusted
to give response to the incoming signal which has 20 times the strength of an interfering
signal and furthermore the desired signal is amplified ten times by each oscillation valve, it is
self-evident that the interfering signal will practically disappear in the circuit of the last bulb.
The circuit of Fig. 296 can be made responsive to undamped oscillations if the tertiary
circuit of valve No. 3 is shunted by an inductance and capacity. With this connection the
amplified incoming oscillations interact with the locally generated oscillations and produce
a beat current in the usual manner.
The student should note that the valves in Fig. 296 have a source of direct current
electromotive force in series with the grid to fix definitely the potential of the latter in
respect to the filament and also that the third valve has a source of E. M. F. in shunt to the
grid condenser to prevent the accumulation of excessive potentials on the latter. This pre-
caution is usually necessary with extremely highly exhausted vacuum valves.
The transformers, P-l and P-2, shown in the diagram, are radio-frequency transformers
shunted by variable condensers of small capacity for obtaining conditions of resonance.
227. The Goldschmidt Tone Wheel. — The mode of operation of this
detector during the reception of undamped oscillations will be more readily understood by
reviewing certain facts in connection with the functioning of the ordinary tikker. When
the tikker interrupts (periodically) the secondary circuit of a receiving transformer tuned
to a distant transmitter, the interruptions do not take place in synchrony with the incoming
oscillations. The telephone condenser, therefore, receives an irregular charge which, at one
instant, may be taken at the peak of the charge accumulated in the secondary condenser,
and, at another instant, at a charge of lesser value, the final result being the production of a
note in the telephone of irregular pitch which is not highly pleasing to the ear.
The Goldschmidt tone wheel overcomes this defect by converting the incoming oscillations
into an audio-frequent current. To illustrate its mode of operation we may assume
that signals are being received from the high-power station at Tuckerton, New Jersey, the
normal wave length of which is 7,400 meters corresponding to an oscillation frequency of
40,540 cycles per second. Now, if a specially constructed mechanical circuit interrupter
giving 40,540 interruptions per second is connected in the receiver circuit in place of the
usual tikker, the positive half, let us say, of each successive cycle will be interrupted at the
peak, such as A, B, C, D, E, etc., Fig. 297, and the current of successive negative halves
only will be admitted to the receiving telephone. There will then pass per second through
RECEIVERS FOR UNDAMPED OSCILLATIONS OR WAVES.
285
the receiving telephone 40,540 pulses of direct current, but, owing to their rapid rate, these
pulses do not individually affect the receiver diaphragm, except when the current is turned
on and off.
If the circuit interrupter be driven to give, for example, 39,540 interruptions, the result
will be that indicated in the curves, Fig. 298a (not scaled) where alternation A is inter-
rupted directly at the peak, al-
* B c D E . f ternation B further down the
peak, alternation C still further
down, and so on.
Now, when a positive alter-
nation is interrupted at the
peak, the full amount of nega-
tive current is admitted to the
head telephone and when a
negative alternation is inter-
rupted at the peak, the full
amount of the positive current
Fig. 297— Effect of the Goldschmidt Tone Wheel When Driven
Synchronously.
is admitted to the telephone (note also Fig. 298b). As the positive alternation is interrupted
at points off the peak, a smaller amount of negative current and a larger amount of positive
current will be admitted and the net result of this will be a decrease of telephone current
as the zero axis (Fig. 298a) is approached.
When the interruption of the incoming oscillation takes place at the zero axis, equal
amounts of positive and negative current (G and G-l, Fig. 298a) will be admitted to the
telephone and there will
be no deflection of the
telephone diaphragm. As
the interruptions con-
tinue beyond this point,
positive current of grad-
ually increasing strength
will be admitted to the
telephone until the full
A' B c' o' E' F 6' amount of positive cur-
Fig. 298a— Effect of the Tone Wheel When Driven As-synchronously. rent flows. There is thus
seen to flow through the
telephone, an audio-frequent current which rises, falls and reverses uniformly at a frequency
which is .the numerical difference of the interruptions of the tone wheel and the frequency of
the incoming oscillations.
The resulting note in the telephone is found to have a musical pitch which can be varied
over a range equivalent to frequencies lying between 200 and 3,000 cycles per second.
In the diagram, Fig. 298b (not scaled), the interruptions of the positive and negative
incoming oscillations are shown by the curve A, D, and the amplitude of the telephone current
by curve B, C. The peak
of the dotted curve is the
point at which a positive
alternation is interrupted
at the peak, and, as
shown by the peak B, the
audio-frequent current is
negative and at a maxi-
mum. The peak D is the
Fig. 298b— Showing Superposed Audio-frequent Current. P.°int ™here .a negative
alternation is interrupted
at the peak and the telephone current, as shown by peak C, is seen to be positive and at a
maximum. At all other points on the curve, the strength of the periodic telephone current
will be less varying as the relative amounts of positive and negative current admitted to
the telephone by the tone wheel.
To produce a note of audio-frequency from the Tuckerton transmitter at its present wave
length, a toothed wheel interrupter having 800 contact segments revolving approximately at
3,000 revolutions per minute would be required. This would interrupt the receiver circuit
39,450 times per second, which would give a note equal to the pitch of 1,000 per second.
286
PRACTICAL WIRELESS TELEGRAPHY.
The tone wheel is frequently termed a frequency transformer because it converts me-
chanically the oscillations of radio-frequency into current of audio-frequency. It is superior
to the ordinary tikker, first, because it produces a musical pitch so highly desirable for
aurul reception, and, second, it converts more energy of the incoming oscillations into useful
sound than does the tikker.
A photograph of the Goldschmidt tone wheel appears in Fig. 299. The commutator disc
of this detector is driven at speeds approximating 4,000 revolutions per minute.
Fig. 299— The Tone Wheel Installed at the Tuckerton Station.
228. Marconi System for Reception of Undamped Oscillations. — The
diagram of connections, Fig. 300, covers the systems for the reception of un-
damped oscillations, developed by Signor Marconi and H. J. Round.
Ttkphont
Fig. 300— Marconi's System for the Reception of Undamped Oscillations.
The circuit in general contains the fundamentals of the Marconi balanced crystal re-
ceiver, and, as explained in a previous paragraph, if crystal No. 1 and crystal No. 2 are
adjusted independently to the maximum degree of sensitiveness, they will produce practically
equal and opposite effects, resulting in the production of no sound in the head telephone. 1
potentiometer P-2, let us say, is adjusted so that crystal No. 2 is in a non-conductive state
to signals, they will be received at moderate strength on crystal No. 1. However, very strong
RECEIVERS FOR UNDAMPED OSCILLATIONS OR WAVES. 287
impulses of static or atmospheric electricity will cause both crystals to become equally con-
ductive resulting in the almost complete elimination of this interference.
To make this apparatus receptive to undamped oscillations, a circuit J, C-l, C-2, C-3, C-4,
is provided, which is acted upon by the buzzer energized inductance B. The voltage set up in
J alters the conductivity of the crystals in the following manner : Crystals No. 1 and No. 2
are adjusted to oppose one another in the usual manner, but the potentiometer voltage is
adjusted so that only very strong signals can be recorded. Now if circuit B is adjusted to a
very short wave, the electromotive force induced by the buzzer acts for short intervals on
the two crystals, making them conductive for a brief period, and thereby releasing the energy
stored up within the condenser K, in accordance. Condenser K is, of course, constantly
charged by the undamped oscillations induced in the receiving aerial. If the groups of
waves from the buzzer have a slightly different period or a submultiple of the initial fre-
quency of the incoming oscillations, an audio-frequent current will flow in the head telephone.
For example, if the frequency of the incoming oscillations is 50,000 cycles per second and
the buzzer produces 4,900 groups of oscillations per second, the result will be a musical tone
in the head telephones having a pitch equal to 1,000 per second.
These circuits have been used by Marconi and his assistants for the reception of signals
over very great distances.
PART XVI.
MARCONI TRANSOCEANIC
RADIO TELEGRAPHY.
229. MARCONI DEVELOPMENT AND GENERAL CONSIDERATIONS.
230. MARCONI'S DUPLEX SYSTEM. 231. THE BALANCING OUT
AERIAL. 232. GLACE BAY-CLIFDEN STATIONS. 233. MARCONI
DIRECTIONAL AERIAL. 234. MARCONI TRANSOCEANIC STA-
TIONS. 235. MARCONI TUBULAR MASTS. 236. RADIO-FRE-
QUENCY CIRCUITS OF THE DAMPED WAVE TRANSMITTERS. 237.
OTHER U. S. HIGH POWER STATIONS. 238. LONG DISTANCE
RECEIVING SETS. 239. CONDENSED LIST OF HIGH POWER
STATIONS.
229. Marconi Development and General Considerations. — The greater
share of credit for establishing radio communication over extremely great dis-
tances, is directly due to the energetic and painstaking experimenters, Marconi and
his staff of engineers. Realizing at an early date that the commercial utility of
wireless telegraphy was not
confined to ship to shore
communication alone, Sig-
nor Marconi began the con-
struction of powerful sta-
tions on both sides of the
Atlantic as early as 1901.
The first high power sta-
tions for trans-oceanic com-
munication were established at
Poldhu, Cornwall, England, and
South Wellsfleet, Cape Cod,
U. S. A., but, as was antici-
pated, these stations were re-
quired solely for the dispatch of
traffic to ships at great dis-
tances at sea and, therefore,
other sites were selected as
soon as possible at Glace Bay, Nova Scotia, and Clifden, Ireland.
A number of experiments were carried out at this station, seemingly insurmountable ob-
stacles were overcome and, by continued application and research, an efficient transmitter
and receiver were finally developed, which could be depended Upon for 24-hour communica-
tion between these two points.
An unfortunate fire at Glace Bay, Nova Scotia, in 1909, delayed the further use of these
stations for several months, but in the process of rebuilding a more efficient station was con-
structed, which has been in commercial service continually since that time.
The work of designing wireless stations such as the Marconi Company have
erected for trans-oceanic work is essentially an enlargement of the work in con-
nection with the sets of only a few kilowatts used for ship and shore stations.
The engineer cannot, however, sit down with a slide rule and multiply the figures
Fig. 300a — Early Marconi Station at Glace Bay, Nova Scotia.
MARCONI TRANSOCEANIC RADIO, TELEGRAPHY. 289
for his calculations relating to the small stations by a hundred or so, and have as
a result a station that will work over a long range. Many problems present them-
selves in a large radio installation which require much care and experimentation
adequately to cope with the requirements of high power transmitters and which,
in smaller sets, are of so little importance as to be practically negligible.
The reader, to assure himself that the construction of the high power stations is an
engineering proposition of the highest order, need only consult the accompanying photo-
graphs showing in a very small part, the apparatus in use at certain of the Marconi Sta-
tions in the United States and abroad. Not only were the technical problems encountered
in their construction broad in their scope and somewhat unusual, but the erection of masts
and building, the transportation of materials, the furnishing of water supply, sanitation,
the provision for power, the housing of employees, etc., each brought their individual prob-
lem which required most painstaking calculations and, in some cases, the provision of
new means to overcome.
It is not adequately possible in the space at our disposal to go over the details of con-
struction of the various Marconi high power stations, but a brief description of the equip-
ment will be given, together with such additional information as may make clear the
general plan of these stations and the method of operation.
As explained in Chapter XIV, both continuous and discontinuous wave systems
are employed for long distance radio communication, and we should add that
either system has its advantages. It cannot be denied that undamped oscillations
give better syntonic effects at the receiver, but almost equal selectivity can be ob-
tained by feebly damped oscillations.
Generally, undamped wave transmitting apparatus requires very careful-adjust-
ment and is not continuously operative over extended periods without very frequent
attention, whereas the spark transmitters, even of 500 K. W. capacity, can func-
tion over very extended periods with only nominal care.
The general trend of development in the United States, however, seems to be
in the direction of undamped wave transmitters which, more and more, are being
put to commercial use. The final result of experimentation in this direction cannot
be foretold, but the results already obtained seem to indicate that even short wave
undamped oscillation generators may shortly be available.
230. Marconi's Duplex System. — A complete resume of the series of ex-
periments which made trans-oceanic communication possible, would in itself con-
stitute a volume of no small proportions, but one of the unique features of the
Marconi high power stations, Which has doubled the volume of traffic that can be
handled from continent to continent, with a given set of stations and has con-
tributed to the prevention of traffic interruption by outside interference, is Mar-
coni's Duplex System, combined with his "balancing out" aerial.
The mode of operation of his Duplex System can perhaps be better understood
by citing a particular example of commercial use. As already mentioned, the Mar-
coni high power station at Glace Bay, Nova Scotia, transmits to another high
power station at Clifden, Ireland, but in order that traffic may be dispatched in
"both directions simultaneously additional receiving stations have been erected on
both sides of the Atlantic, a few miles distant from either transmitting station. This
separation of stations would not in itself prevent interference between the trans-
mitter and receiver, but by combining this plan with the balancing out aerials inter-
ference is wholly prevented.
The transmitter at Glace Bay, Nova Scotia, is approximately 30 miles north of the
receiving station located at Louisburg, Nova Scotia, while the receiving station for the
opposite side is at Letterfrack, Ireland, approximately 12 miles north of the transmitter
at Clifden, Ireland.
With this separation of transmitter and receiver, Glace Bay station, for instance, may
dispatch messages to Letterfrack freely and not interfere with Louisburg station receiving
from Clifden, Ireland1. Not only may this system be used for simultaneous transmission
in both directions, but it can be used as a "break-in" system as well, permitting the receiv-
290
PRACTICAL WIRELESS TELEGRAPHY.
ing operator to break in on the sending operator, asking for the repetition of a word,
a letter or a sentence if necessary.
Now that the general plan of the Duplex System has been explained, the reader should
refer to the diagram, Eig. 301, showing in a more detailed manner the operation of the
Duplex System in a specific instance, viz., as employed on the Glace Bay-Clifden route.
The 150 K. \V. transmitter at Glace Bay, Nova Scotia, connected to aerial A, B, is
designated as station Xo. 1. Operated at the wave length of 8,000 meters, this station
transmits to Letterfrack, Ireland, direct, designated as station No. 2.
The transmitter at Clifden, station No. 4, transmits to Louisburg station No. 3 at the
wave length of 5,500 meters.
5 5000 METER WA\/E
GLACE BAV N s
TRANSMITTED STATION N»
LETTtRFRACK IRELAND
RECEIVER RATION N? 2
5500 METER WAVE
LOUISBURG N 5
RECEIVER STATION
CLIFDE.N IRELAND
TRANSMITTER STATION N
Fig. 301 — Marconi's Duplex High Power Transmitter Scheme With Balancing Out Aerials.
Stations No. 1 and No. 3 are connected by wire line, similarly, stations No. 2 and No. 4.
The sending operator for station No. 1 is located at station No. 3, the transmitter at No. 1
being actuated by a manually operated key or automatic sender, the circuit of which ex-
tends over the wire line connecting the two stations.
Similar arrangements are in- use on the opposite side of the Atlantic, the transmitter
at Clifden, Ireland, being controlled by an operator stationed at Letterfrack. Both the
transmitting and the receiving operators may thus work side by side, traffic being dis-
patched freely in both directions. But to positively insure against interruptions of service,
the transmitting stations are equipped with receiving sets, to be employed in event of a
breakdown at the regularly appointed receiving stations.*
*The general scheme and mode of operation of the high power stations herein described is that
originally planned. This is not necessarily the way these stations are now operated. Changed conditions
dre to the European situation have required some re-arrangement of the original plan and method.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
291
231. The Balancing Out Aerial. — It will be well to understand that al-
though transmitting stations No. 1 and No. 4, Fig. 301, operate at wave lengths of 8,000
meters and 5,500 meters respectively, some of the energy of the 8,000 meter wave is apt to
induce oscillations of its own frequency in the receiving aerial, C, D, station No. 3, when the
latter is adjusted to the wave length of 5,500 meters.
In the same manner, station No. 4 would induce oscillations in the receiving aerial at
No. 3, setting up no small amount of interference, were it not for the use of the balancing
out aerials, E, F, and E1 F1 at stations No. 3 and No. 2, respectively.
These balancing aerials are generally located at a right angle to the main receiving
aerial in such a way as to receive the maximum induction from the nearby transmitter and
the minimum induction from the far distant transmitter.
The circuit of the balancing aerial is tuned to the interfering wave and inductively op-
posed to the interfering oscillations induced in the main receiving aerial at the secondary
winding. Tlien by proper adjustment of coupling and phase relation of currents, the energy
induced by the interfering wave is electro-
magnetically balanced out, leaving the
main receiver aerial free to receive from
the far distant transmitter.*
In the diagram, Fig. 301, aerial C, D,
for instance, at station No. 3, is favor-
ably disposed for the reception of signals
from aerial A1, B', and the balancing aerial
E, F, receives the maximum induction
from A, B, and the minimum from A1 B1.
Similarly, balancing aerial E1, F1, re-
ceives the maximum induction from A1,
B1, and the minimum induction from A,
B. If oscillations be induced in C, D,
by the 8,000 meter wave from A, B, and
thereby cause interference to the recep-
tion of signals at the wave length of 5,500
meters from A1, B1, the balancing aerial
E, F, is tuned to 8,000 meters and its
circuit inductively opposed to the secon-
dary of the tuner connected to C, D.
Proper adjustment of coupling and de-
crement permits the oscillations (induced
by the 8,000-meter wave in each) to be
brought opposite in phase, and the inter-
fering signals thus balanced out, signals
being received all the while from A1, B1.
In practice, this System has been found F'g- 302 — Fundamental Circuit of the Glace Bay Type
to work well, preventing the transmitter
and receiver from interfering with each other, although separated no more than 8 or 10 miles.
232. Glace Bay-Clifden Stations. — We have already intimated that the
installation and the subsequent successful operation of the Glace Bay and Clifden
high power stations opened up a new era in long-distance communication. In view
of the pioneer work performed at these two points, it may be of interest to de-
scribe fundamentally the transmitters in use.
Contrary to previous installations, the condensers were charged by 14,000 volts direct
current, the source of which was a battery of 6,000 storage cells connected in series. These
batteries in turn are charged by three 5,000-volt generators (A, B, C, Fig. 302), of very
special construction, connected in series and then to the terminals of the battery.
As will be seen from the fundamental diagram, Fig. 302, the energy stored up in the
condenser C-3 is discharged through the usual oscillation transformer and Marconi's studded
disc discharger.
This discharger consists of a large steel disc several feet in diameter, with sparking
electrodes mounted thereon and1 which pass closely to the fixed electrodes B, B.
DI5C
DISCHARGER
See Section I Appendix.
292 PRACTICAL WIRELESS TELEGRAPHY.
The electrodes B, B, in reality revolve slowly, and therefore present constantly cooled
surfaces to the path of the spark discharge. Protective chokes C-l and C-2 protect the
generator from the discharge of the condenser.
The principal advantage of the disc discharger is the quenching effect obtained when the
disc is driven at a certain velocity. This prevents the re-transference of energy to the
spark gap circuit, and in consequence, the antenna oscillations have a decrement as low as
.03 per complete cycle. In addition a spark or group note of distinct musical pitch is obtained
which has been found extremely desirable for aural reception through atmospheric electricity.
The high potential condensers at both of these stations are of unusual construction and
dimensions. Consisting of a number of large steel plates suspended from the ceiling on
special insulators, they are separated sufficiently to prevent the spark discharging between
plates, and the required capacity is found in connecting a large number of such plates in
parallel.
Beyond the size of this condenser, the oscillation transformer comes in for attention,
principally because of its dimensions. The primary winding has but two turns, consisting
of a specially constructed cable, one foot in diameter. Owing to the large amounts of
power in use, a cable of these dimensions is positively required, and good surface conduc-
tivity is among the chief considerations.
Signalling is not effected by interruption of the primary circuit as in small-sized Marconi
transmitters. In these sets, specially constructed high voltage relay switches (S-2), in turn
controlled by a small telegraph key and source of D. C. current, interrupt the high voltage
circuit from the battery to the condenser. Arcing is prevented by forcing an extra heavy
air blast on the contact points by specially designed motor blowers.
The receiving apparatus at these stations may either consist of a Marconi balanced crys-
tal receiver, employing the carborundum rectifier, or a set of Fleming vacuum tubes of
special design, type and construction. Through a set of microphonic relays, connected in
cascade, the signals may be amplified considerably and either deciphered in an ordinary ear
telephone or the pulsations of current may be indented on the wax records of a dictaphone.
233. Marcohii Directional Aerial. — The great success of Signer Marconi's
Trans-oceanic system is in no small measure due to the use of the horizontal direc-
tional aerial* Fully convinced by a series of quantitative experiments that the
flat top aerials radiate more freely in the direction opposite to which the free end
points, particularly if the length of the flat top exceeds the length of the vertical
portion by four or five times, Signor Marconi decided that the adoption of this
aerial would not only permit the transmission of messages over great distances
with small powers but also on account of its directional properties would prevent
a considerable amount of interference to the operation of other stations.
In the same series of experiments, it was determined that a flat top aerial receives with
greater intensity when the free end points in the direction opposite to the free end of the
transmitter aerial. Irrespective of its selective directional properties, a horizontal aerial
of given capacity and inductance for any required wave length, is less expensive to erect
than a vertical aerial of similar electrical dimensions ; hence, from this consideration alone,
the flat top aerial is the one that would be adopted.
In order to radiate the energy of a 300 K. W. transmitter, the aerial should have a
fundamental wave length of at least 6,000 meters ; in fact the greatest distances are covered
when such aerials radiate near to their fundamental wave length.
The great Marconi station at New Brunswick, New Jersey, U. S. A., for example, has
an aerial of 32 wires connected in parallel, 5,000 feet in length. The aerial is supported by
12 tubular steel masts, 400 feet in height, arranged in two rows of six each. The funda-
mental wave length is approximately 8,000 meters, but the initial transmitting experiments
were carried on at the wave length of 15,000 meters.
The receiving aerial for this station at Belmar, New Jersey, consists of two wires 6,000
feet in length, suspended on six tubular masts, 400 feet in height. The aerial has a general
direction favorable for reception from the giant transmitting station at Carnarvon, Wales.
234. Marconi Transoceanic Stations. — By far the greater number of high
power radio stations here and abroad have been designed and erected by the
*An explanation of the cause of the unsymmetrical radiation of an inverted L aerial appears in
Page 167 of Fleming's Elementary Manual of Radio Telegraphy.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY. 293
Marconi Company. In fact, their stations only have maintained a continuous
operating schedule from day to day, from continent to continent. Individual con-
cerns may have carried out spectacular experiments here and there, but nothing
has been evolved by them that would tend to make long-distance communication
a success commercially. The mere fact that a message may, for instance, be sent
across the ocean by a low-powered transmitter and received on a small aerial at
certain hours of the day is no indication that such equipment could be used for
continuous 24-hour service, because experiment reveals that very large powers
are required for continuous operation, when the sender and receiver are 3,000
miles apart.
Those who are familiar with the great globe-girdling scheme of the Marconi Company
cannot help but be impressed with the stupendous undertaking involved in the construction
of their high power stations, for not only is the task of d'esigning the apparatus, buildings
and power machinery one of extraordinary undertaking, but the actual installation of such
has, in many instances, called for painstaking labors and effort largely due to the location,
the nature of the soil, and the topography of the surrounding country.
In view of the universal interest manifested by students of radio in behalf of high power
radio stations of the Marconi Company, a brief description of their equipment will be pre-
sented, together with such additional information, as will make clear the general plan and
mode of operation. First let it be explained that although these stations could all be
made intercommunicative, it is more usual to construct a pair of stations to cover a specific
route or to join together two continents only.
With the idea in view of showing which of these stations was intended for
communication with the other, they shall be grouped into ''radio circuits" or routes,
as follows :
CIRCUIT NO. 1.
Stations sep-f Glace Ba£ *£? Scotia"' transmits t0"- Lett*rfrack> ] Stations sep-
arated about^ Louisb No;a Scotia... receives f rom . . . Clif den, fara£d ..about
Ireland.
Since the apparatus for the Glace Bay station has been very briefly described in para-
graphs 274 and 275, it will not be gone over again, except to mention that the Duplex Sys-
tem has been installed and thoroughly tested. Because these two stations established the
first successful trans-oceanic commercial radio service, they are purposely grouped at the
head of the list.
CIRCUIT NO. 2.
C New Brunswick, N. J., U. S. A transmits to "1 Qfofl-
ab^J Towrn? Wales, Great Britain, fe"8 .££
50 miles [ Belmar' Waje'sU' S' A" ' '"""" fr°m- ' -C^"3™"' j 62 miles.
The transmitting station at New Brunswick is of 300 K. W. capacity and can be operated
at various wave lengths from 7,000 to 15,000 meters. Power is taken in the station from a
commercial power house at 1,100 volts, 3 phase 60 cycle alternating current, stepped down
to 440 volts and led to the terminals of a 60 cycle, 440-volt 3 phase 550 H. P. motor, which
drives a 300 K. W. 120 cycle generator.
The current is led from the generators to a bank of high voltage transformers, the sec-
ondaries of which may be connected in series or in parallel according to the power required.
In the usual manner the current from these transformers charges a large bank of high
voltage oil plate condensers which, in turn, discharge through an oscillation transformer
and rotary disc discharger of uncommon proportions. As in the Glace Bay Station, the
circuit from the transformer secondaries to the condenser is interrupted by a specially
designed set of high tension relay keys which, in turn, are actuated by a small sending key
and a source of direct current.
Arcing at the contacts of the main signalling key is prevented by a heavy blast of air
forced directly at the contact points by specially designed motor blowers. The advantages
294
PRACTICAL WIRELESS TELEGRAPHY.
derived in interrupting of the high voltage current, lies in that it permits 300 K. W. to be
handled at various speeds of transmission up to 100 words per minute without error.
A more detailed description of certain apparatus of the circuits of radio frequency for
the Xew Brunswick station and others -with like equipment (damped wave apparatus) will
be given in paragraph 236.
Fig. 303 — Power House of the Trans-Atlantic Marconi Station at Carnarvon, Wales.
The transmitting aerial at the New Brunswick station is of the inverted L type, consist-
ing of 32 wires with a flat top approximately 5,000 feet in length. It is supported on two
rows of steel tubular masts (6 masts in each row), which are approximately 400 feet in
height. The two rows of masts are separated about 250 feet.
The receiving aerial at Belmar is 6,000 feet in length, consisting of 2 wires supported
on six tubular masts, each 400 feet in height.
Fig. 304 — Motor Blowers at Carnarvon Station.
The transmitter at Carnarvon, Wales, is substantially a duplicate of the New Bruns-
wick transmitter, the source of power being a 300 K. W., 150 cycle motor generator
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
295
with step-up transformers, oil condensers, etc. Of late, a 150 K. W. timed spark discharger,
excited hy 5,000 volts continuous current, has been employed as well, and with which par-
ticularly successful results have been obtained. Operated usually at the wave length of
10,000 meters, daylight communication has been established with the U. S. A., the strength
of signals being equal to that obtained from other foreign stations of much greater power.
(For a more detailed explanation of timed spark discharger sets see paragraph 219.)
Some idea of the construction of the Marconi high power stations may be ob-
tained from the following description:
The power house of the transmitting section of the Wales Transoceanic station at Car-
narvon, Wales, is shown in Fig. 303, wherein the aerial and ground leads of the great
antenna which transmits messages to the Belmar, New Jersey, station appear prominently
in the foreground. This building measures approximately 100 feet by 83 feet, and is divided
into three sections, known as the main machinery hall, the annex, and the extension. The
Fig. 305 — Three Hundred Kilowatt 150 Cycle Generators at Carnarvon Station.
transmitting sets, switchboard, transformer room, stores, offices and emergency operating
room are located in the main machinery hall. The auxiliary plant is placed in the annex,
consisting essentially of D. C. generators, electrically driven blowers and ventilating fans,
and some small motor generator sets used in the signalling circuit. An office for the engi-
neers and a fitting shop are also provided for in the annex. The extension is devoted
entirely to experimental apparatus. All trans-Atlantic wireless messages transmitted from
this station will be handled automatically from London, through the receiving section at
Towyn, sixty-two miles away, and received at Belmar for automatic transmission to New
York. This station is therefore of great interest to Americans as the communicating links
with the New Jersey stations in the Marconi globe-girdling chain.
In Fig. 304 are shown the blowers which furnish air under considerable pressure, to blow
out the spark at the disc discharger and keep the disc elements cooled. These are also used
to blow out the sparks at the signalling switches which relay the dots and dashes to the
aerial wires.
In Fig. 305, the 300 K. W. 150 cycle motor generators at the Carnarvon station are shown
as installed ready for use. In the photograph, Fig. 306, are shown the signalling motor gen-
erators and the disc motor starters at Carnarvon. One of each is a spare. The signalling
motor generator supplies current to work the high speed relay switches through which the
station is enabled to transmit from a distant operating station at the rate of 100 words a
minute. The motor starters shown on the right control the 75 H. P. motors, which drive the
296
PRACTICAL WIRELESS TELEGRAPHY.
disc discharger when it is disconnected from the main generator for as-synchronous working.
Photograph, Fig. 307, gives a view of the high voltage transformers and primary induc-
tances. All the current from the generators passes through the transformers, where it is
stepped up to a voltage
_ sufficient to charge the
condensers. The low
frequency inductances
shown to the right of the
drawing permit a large
range of adjustment in
the primary power cir-
cuits, thereby permitting
the radiated energy to be
controlled in accordance
with the requirements.
Fig. 308 shows the
switchboard at the New
Brunswick, New Jersey,
station. This board con-
trols the generator cir-
cuits, blower machinery
and all controlling appli-
ances within the station.
The receiving station
at Belmar, New Jersey,
is completely equipped with a Marconi balanced crystal receiving set, Brown amplifying relays,
a balancing out aerial for eliminating interference, dictaphone receivers, and a set of
telegraphic instruments for connection with the land line telegraph and telephone companies.
These transmitting and receiving stations not only have the necessary buildings for the hous-
ing of the apparatus, but hotels and individual dwellings are supplied for the employees as
well.
Fig. 306 — Special Signalling Generators at Carnarvon Station.
Stations
arated
30 miles.
*ep7 f Marion, Mass.
)out Chatham, Mass.
CIRCUIT NO. 3.
.transmits. . . Stavanger,* Norway,
.receives from. . .Naerboe, Norway.
Stations sep-
arated about
30 miles.
At the writing of this volume, this group of stations are under construction and very
nearly completed. They will be used for 24-hour commercial working and will permit com-
munication with Northern European countries, independent of all existing routes, obviating
the necessity for a number of intermediate relay points.
The transmitter at Marion will be a 150 K. W. Marconi timed-spark continuous wave
generator, energized by a 300 K. W. 5,000 volt D. C. generator. The transmitter at Stavanger
will be substantially a duplicate, with ultimate capacity of 300 K. W. Since they have been
found the most economical and practical for the purpose, the aerials at« these stations are
supported by tubular steel masts. As usual, the stations are constructed for Duplex working,
Marion and Chatham as well as Stavanger and Naerboe stations, being con-
nected together by land line control. These stations will be placed in commercial operation
within a very short time.
CIRCUIT NO. 4.
04.04.;,™ r Bolinas, Calif .... transmits to...Koko Head, 1 ,
abou1; J Hawaiian Islands, I Statl°ns *eP-
>OUt 1 Manshalls, Calif. ... receives from. . .Kahuku, Ha- f arated about
25 miles.
40 miles.
Stations sep-
arated about
60 miles.
waiian Islands.
CIRCUIT NO. 5.
r Kahuku, Hawaiian Islands . . . transmits to ... Funa-
bashi, Japan,
j Koko Head, Hawaiian Islands . . . receives from . . .
Funabashi, Japan.
*Station is located at Hinna.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
297
Because the transmitter at Kahuku is duplexed for simultaneous transmission to Japan
and the U. S. A., the two circuits, No. 4 and No. 5, have been grouped together. Beginning
with the Bolinas station, the transmitter is of 300 K. W. capacity, current for its operation
being supplied by duplicate 500 H. P. steam turbine driven generators delivering current at
180 cycles per second. In the usual manner, this current is stepped up by closed core trans-
formers to approximately 50,000 volts and employed to charge a bank of high voltage oil
plate condensers. Although normally operated at from 75 to 150 K. W. the full 300 K. W.
can be employed whenever necessary.
The aerial for receiving from Bolinas, Cal., is nearly a mile in length erected on two
rows of tubular steel masts in the usual manner. The receiving aerial at Marshalls, Cali-
fornia, has 7 masts, each of which are 330 feet in height.
The receiving station at Koko Head, Hawaiian Islands, has two distinct receiving aerials,
together with balancing out aerials, one being employed for reception from Bolinas, Calif.,
and the other from Funabashi, Japan.
Fig. 307 — Bank of High Voltage Trans- Fig- 308 — The Switchboard of the New Brunswick
formers at Carnarvon Station. High Power Transoceanic Station.
The aerial for receiving from Bolinas extends southwestward from the operating house
and is carried on five 330 feet masts to an anchorage on the beach. The aerial for
reception from Japan extends from the operating room almost due east. The first
two masts for this aerial are of the standard sectional type 430 feet in height; the first is on
level ground and the second is on the hillside. From this point the aerial makes a long span
of over 2,000 feet to the top edge of Koko Head (an extinct volcano) at an elevation of 1,194
feet above the sea level ; here there is not enough room to erect a sectional mast, only about 40
square feet being available for a self-supporting structural tower 150 feet in height. The tail
end anchorage for this aerial is far down the volcano on the inside of the crater. The balanc-
ing aerial, which is employed for both receiving aerials, is erected on self-supporting towers,
each of which is 100 feet high. All this will be clear from the diagram, Fig. 309, wherein a
298
PRACTICAL WIRELESS TELEGRAPHY.
complete lay-out of the receiving station at Koko Head appears showing the relative posi-
tions of the balancing out aerial, the location of buildings, etc. It is to be noted that the
balancing out aerial is 5,700 feet in length, and is arranged to be favorable for the absorp-
tion of energy from the two transmitting stations at Kahuku.
Because it is duplexed for the simultaneous transmission of messages to Japan and the
United States, especial interest attaches to the Marconi station at Kahuku, Island of Oahu.
Hawaiian Islands. Not only is this station fitted with two 300 kilowatt transmitting sets but
a third emergency set has been installed as well, which in event of breakdown can be con-
nected either to the Japan or the United States aerial.
The general layout of the antennae and buildings at Kahuku is shown in the diagram,
Fig. 310, wherein it will be noted that the free end of these aerials point in a direction
RECEIVING STATION
KOKO HEAD
ISLAND or OAHU
Fig. 309 — Plan and General Layout of the Receiving Aerials at Koko Head, Hawaiian Islands.
favorable for the particular continent with which communication is to be established, being
designated as the "Japan" aerial and the "San Francisco" aerial.
From the power house as a center, the California transmitting aerial extends southwest-
ward, supported by twelve masts, 325 feet in height; the Japan aerial extends to the south-
east, supported by fourteen masts, 475 feet in height. These masts are the largest that have
been yet constructed on the Marconi system of sectional cylinders. The power house con-
sists of boiler room, engine room and condenser room. The boilers are oil-fired and will
feed three 500 H. P. turbines, which drive the special 300 K. W. alternators and Marconi
disc discharger.
The necessary condenser capacity for all three transmitting sets is "found in 768 large
oil tank type condensers, which are conveniently arranged for uniform distribution of current
to all connecting bus bars.
The automatic sending and receiving apparatus plays an important part in the service
between the Occident and the Orient. The sending machine consists of a Wheatstone auto-
matic transmitter and special perforator, which makes possible the transmission of more
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
299
than 100 words a minute. Under the automatic system, ten or 100 messages can be filed
at the same time at the office of the Marconi Company in Honolulu. They will be distributed
among the necessary number of operators and the dots and dashes punched in a paper
tape by a typewriter perforator This tape is fed into an automatic sender and the signals
conveyed by land line to Kahuku, where the dots and dashes actuate a high voltage sending
key, automatically energizing the aerial instantaneously with the feeding of the tape in the
station, thirty miles or more away. At the transmitting station the dots and dashes operate
the magnets of the high power sending key in the main energy circuits and the signals are
TRANSMITTING STATION
KAHUKU
ISLAND or OAHU
LOG AT i
Fig. 310 — General Plans of Transmitting Aerials at Marconi Station, Kahuku, Hawaiian Islands.
flashed to whichever destination the message calls for — either Marshalls or Funabashi. If
the message is destined for Marshalls it will be received on a specially constructed dicta-
phone machine, each cylinder, as soon as it is indented with dots and dashes, being handed
to an operator, who transcribes it into a typewritten message by means of a reproducing
dictaphone machine, running at normal speed.
The Imperial Japanese Government station at Funabashi, Japan, is equipped with a
200 K. W. quench spark transmitter, but complete details of the equipment are not yet
available.
235. Marconi Tubular Masts. — One of the most interesting features of the
original construction work at the Marconi high power stations was the erection of the steel
tubular masts, the successive stages of erection being shown in Figs. 311, 312, 313, 314 and
315. The mast is made up of steel cylinders (Fig. 311), constructed in quarter sections,
flanged vertically and horizontally and secured together by bolts stayed with steel cables.
These stand in a concrete foundation. Surmounting the main steel column was a wooden
top mast, the lower part of which is squared and set in square openings in the plates between
300
PRACTICAL WIRELESS TELEGRAPHY.
Fig. 311— Showing Steel Semi-Cylinders for
the Marconi Tubular Mast.
the steel cylinders. The hoisting arms attached
to the upper end were fitted with blocks and
hoisting cables. Attached to these arms were
chain hoists supporting a square wooden cage
(Fig. 312) for the workmen, which was lowered
or raised as the demands of the work required
while the sections were being bolted together.
The wooden topmast was the keynote of
this novel system of construction, operating
like a man who pulls himself up by his boot-
straps. The lower half of this topmast is of
square section and is guided by a square hole
in the diaphragm plates between each section.
The topmast was fitted with a set of hoisting
arms which carried blocks through which reaved the material hoisting ropes. A square
wooden cage was suspended from the hoisting arms by four chain hoists so that the work-
men in it could move themselves up and down to bolt
the sections together. This is more clearly shown in
Fig. 314.
Assume that two cylinders have been bolted to the
bed plate, the mast rising through the center. The sec-
tions of the third cylinder were raised by a steam winch
and bolted in place by the workmen. Then a heavy
flexible steel rope was temporarily anchored at the top
of this last cylinder. Attached to the top of the steel
section, this cable led down inside the cylinders and
around a wheel in the foot of the wooden topmast; then
it was carried up again on the other side and around a
sheave to the top of the steel, thence to the winch. By
pulling on this rope the topmast was raised the length of
one cylinder and pinned through holes in both steel and
wooden masts. With the addition of a new cylinder, the
topmast was raised again, the pin supporting it until this
was brought about (Fig. 313). The stays were attached
at the required points as the erection of the mast
progressed.
The stays, by means of which each mast is supported,
are made of heavy plough steel cable, possessing great
tensile strength. For each mast thousands of feet of this
cable were used, great care being taken to see that the
elastic extension of these stays was not so great as to result in the vibration of the mast
during heavy winds. It was essential to break each stay into short lengths connected with
great porcelain insulators in order that the electrical energy might
not be absorbed, led to the earth by the stays and lost for purpose
of wireless operation. For all connections at the masts, insulators
and anchorages, special bridge sockets were designed. This did
/fff S away with the necessity for splicing and permitted a perfect and
straight pull, thereby developing the strength of the cable. Heavy
concrete blocks were used as anchorages for the stays. The
completed mast is shown in Fig. 315.
In addition to the antennae stretched between the masts, great
quantities of wire were placed in the ground about the stations in
order to provide an efficient earthing system or ground connec-
tion. Told in brief, a circle of zinc plates is buried in a trench,
bolted together and jointed to the wireless circuits of the power
house by copper wires. Wires radiate from the zinc plates in the
ground to a set of outer plates, from which extend another set
of earth wires placed in trenches running the full length of the
aerial. The general scheme for the earth connection is shown in
Fig. 320.
236. Radio-Frequency Circuits of the Damped
stages of Construction! Wave Transmitters. — A description will now be given
Fig. 312 — Showing Workmens' Cage
Which is Carried to the Top
During the Process of Erection.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
301
of certain apparatus of the radio-frequency circuits of the high power transmitting stations
employing apparatus for the production of damped waves.
As in the small station, the principal circuits are simple, but it is easily seen that when
about three hundred kilowatts are to be carried in the circuits and turned into high frequency
currents, the problem must be handled with care. Some of the special arrangements made to
use this large amount of current safely
and efficiently may be of interest to the
student.
The closed oscillating circuit is of in-
terest because of the size and construction
of its various elements. The discharger is
of the rotating-disc type, and is directly
connected to the shaft of the alternator.
The foundation upon which it rests is a
solid block of concrete weighing about
seven tons, supported by piles of insulat-
ing compound in such a manner that the
framework of the discharger is well pro-
tected. The coupling for the alternator
is also insulated, the only live part being
the discs which serve as the poles between
which the studs pass. The spark dis-
charge is well quenched by a blast of air
under high pressure. In order that the
Fig. 314— Showing the Cage and
the Top Mast Several Hun-
dred Feet from Earth. Fig. 315— Completed Mast (Guys Not Shown).
phase relation between the alternator current and the spark may be varied to the most
advantageous point, the alternator is built with the armature frame, the machine being of the
rotating field type, mounted in a secondary outside frame, with a track machined in its
inside circumference. On this track the armature frame may be rotated through an arc equal
to the angle between the poles, by means of a hand wheel. Thus the spark may be made to
discharge the condenser at any desired point of the sine wave. The dischargers are set in
sound muffling rooms and the leads run up through the ceiling to the oscillation trans-
formers mounted on the floor above. These rooms are exhausted by motor-driven blowers
302
PRACTICAL WIRELESS TELEGRAPHY.
r^-i
J1L
SIDE: vie.w
OSCILLATIOM TRA
Fig. 316 — Side View of 300 Kilowatt Oscillation Transformer.
of capacity sufficient to keep the air fresh and to draw out the air, which is admitted by
the high pressure blast used for quenching the spark.
One of the precautions taken to provide an uninterrupted service is to duplicate any and
all pieces of apparatus which are at all likely to be disabled. Thus, two generators and two
disc dischargers are supplied for each station, and a ready means provided to connect either
one to the bus and the oscillation transformer.
PLAN view
OSCILLATION
Fig. 317 — Plan View 300 Kilowatt Oscillation Transformer Showing High Tension Bus-Bar.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
303
As the oscillation transformers are worthy of note, a sketch of them accompanies this
Chapter (Figs. 316, 317 and 318). It will be seen that the coils are mounted on a horizontal
axis and supported on a wooden frame. The primary coil is in series in the closed circuit.
It consists of four turns, each turn being almost a complete ring of about 345 degrees. These
turns are connected by heavy copper plates, making the equivalent of a helix of four turns.
The helix is five feet in diameter (See Fig. 318), and the section of the turns one foot in
diameter. The turns are made of a wooden former, upon which the conductors are grouped.
They follow along the length of the former, but have a long pitch in a spiral direction
laid upon it in such a way that the length of each wire is the same starting from one connect-
ing plate to the next, that is, through the arc of 345 degrees. All the conductors are, in them-
selves, made up of stranded insulated copper wire.
The secondary coil of the oscillation transformer is wound on a wooden former, com-
posed of two end plates with wooden rods, upon which are mounted porcelain spools. On
these spools the con-
ductor is wound; it
consists of fourteen
turns of a specially
built high frequency
cable. The cable is
made by winding
thirty-six small con-
ductors around a
hemp center core,
each conductor being
made of seven double
cotton covered wires.
There is a cotton
cover over the whole
cable, which is about
three inches in diam-
eter. In mounting
this secondary coil
on the frame, the
barn-door type of
roller bearings is em-
ployed. This makes a
device that can be
constructed totally of
Fig.
318 — The 300 Kilowatt Oscillation Transformer Installed at the
Marconi High Power Station at Kahuku, Hawaiian Islands.
wood, and for close adjustment a wooden hand screw is used, which will clamp the coil on
the supporting bar of the frame, as well as furnish the means for adjustment.
From the oscillation transformer, the buses (Fig. 317) are led to the center of the con-
denser room, and as the transformer is on the second floor of the powerhouse, the main
leads are carried horizontally about fourteen feet above the condenser room floor. The
condenser bank is divided into four groups, each group being fed from the overhead buses.
Each group is then subdivided into four sections of twenty-four tanks. They are connected
in parallel series, three tanks being in each series and eight rows of three tanks each in
parallel in each section.
From the central point of the room the overhead buses lead radially to points directly
over the center of each section. Here the leads are carried down to a level with the con-
denser tops. From this point the sections are fed. The main bus is made of twenty-four
inch wide copper, bent in trough shape, the return lead being supported under the other.
At every point where the leads divide, a smaller size conductor is used, and all the leads are
so arranged that the distance between them can be adjusted, in order that the inductance
(of the leads) can be varied as the requirements of the circuits demand. By using this
system of distribution, the path of the current from the oscillation transformer to any tank
in the entire bank of three hundred and eighty-four is exactly the same. This is very im-
portant, in order that no one tank will be required to work on a greater current than any
other. Each section of twenty-four tanks is set on a sloping floor, and from each section
runs an oil drain, under the floor, to a single receiver.
The condenser tanks at the high power stations are modifications of the Poldhu type
shown in Fig. 319. They consist of stoneware tanks, thirty inches high by seventeen inches
wide, by seven inches thick, The design was adopted for the purpose of keeping in view
304
PRACTICAL WIRELESS TELEGRAPHY.
the necessity of the quick and easy replacement of plates. All the elements of a tank can be
lifted out bodily and new plates of glass readily inserted. A fibre sling carries thirty-one
glass plates and twenty-nine zinc plates, every alternate zinc plate being connected to the
buses. . , ' |. i
As will be seen in the sketch, the plates are connected to the terminals by flexible strips,
which compensate for any inequalities in the depth of the tanks. The covers are thoroughly
oil-sealed, and the whole tank is filled with a high grade mineral oil. As the slightest trace
of moisture in the oil renders its insulating value inadequate, and as oil is highly hygroscopic,
it is quite essential to use only very dry oil. To obtain this, a filter press is installed in each
station.
O
CONNECTOR,
CA.OSS SECTION Or TANK..
Fig. 319 — Details of Condenser Tanks for High Power Stations.
If any tank fails or is broken down, the section of which it is a unit is cut out of the
bank, and the spare section cut in. Then a portable derrick is run over the section, and by
means of a block and tackle, which it carries, the contents of the tank are lifted out. To do
this, a pair of tongs are run down through the small holes in the center of the cover, and
the hooks inserted in the holes in the fibre sling. Thus the contents of the tank can be lifted
out with the cover attached, and a new set of elements put in very quickly, without lifting
the tank itself. After this, repairs can be made to the elements at leisure.
MARCONI TRANSOCEANIC RADIO TELEGRAPHY.
305
EARTHING SYSTEM
Hi»w POWER TRA.NSMITTINO STATION
s= GENERAL SCHEME =«s —
THESE EARTH wine's EXTEI.
X
X
Fig. 320 — General Scheme of Earth Connections for High Power Stations.
237. Other U. S. High Power
Stations. — In addition to the Mar-
coni High Power Stations just described,
two additional stations have been erected in
the United States for transocean communi-
cation, which are now under the control of
the United States Government. One is lo-
cated at Sayville, Long Island, and the other
at Tuckerton, New Jersey. In the original
installation, the Sayville transmitter con-
sisted of a 100 K.. W. quenched spark set
operated at the wave length of 4,800 meters,
but in the past two years a 100 K. W.
Joly-Arco undamped transmitter has been
in use and has been operated at a wave
length of 10,000 meters. During the favor-
able hours of the day, communication has
been established with a corresponding sta-
tion located at Nauen, Germany, the latter
station being fitted with a powerful un-
damped wave transmitter.
The station at Tuckerton, New Jersey, is
equipped with a 200 K. W. Goldschmidf
radio-frequency alternator and a 100 K. W
Poulsen arc type of transmitter, both of
which are employed for communication
with a corresponding station at Hanover,
Germany, the latter station being fitted with
a 200 ~K. W. Goldschmidt alternator.
Fig. 321 — The Aerial Tuning Inductances at Kahuku
High Power Station.'
306
PRACTICAL WIRELESS TELEGRAPHY.
Both the SayvilJe and Tnckerton stations employ the unjbrella type of aerial, erected on
masts of great height. The Tuckerton tower, in fact, is 850 feet in height, while the tower
at Sayville is approximately 550 feet high,
and, as is to he expected, the aerials sup-
ported by these towers require a great deal
of space for erection.
In initial experiments at Tuckerton,
New Jersey, the Goldschmidt tone wheel
was employed as a receiver, but of late a
modified form of the oscillating vacuum
valve has been in use, which gives increased
strength of signals. The receiving appara-
tus at Sayville is of the vacuum valve oscil-
lating type, various circuits being used,
generally the type favored by the particular
electrician in charge.
238. Long Distance Receiving
Sets. — Various types of long dis-
tance receivers have been developed by the
Marconi's Wireless Telegraph Company,
Ltd., both for the reception of damped
and undamped oscillations. The high power
stations in the United States are fitted with
balanced crystal or Fleming valve receivers,
the local circuits of which are connected to
3 or 4 microphonic amplifying relays, con-
nected in cascade. By means of these a
considerable amplification of the incoming
signals is obtained, which, in fact, can
frequently be heard with the receivers
lying on the table with the transmitting
station 3,000 miles distant.
Marconi trans-oceanic receiving stations
are also completely equipped with dictaphone
receivers which are arranged so that immediately one wax record is indented with
signals, a second dictaphone receiver is automatically connected in the circuit, and so on.
The use of these records permits traffic to be dispatched across the ocean at speeds, up to
75 words per minute, which is afterwards transcribed on the typewriter by the receiving
operator at speeds varying from 30 to 40 words per minute. Obviously this system will
permit a greater amount of traffic to be handled between two stations and it will, therefore,
be employed when atmospheric electricity is not too severe.
239. Condensed List of High Power Stations. — Some of the long distance
transmitting stations of the Marconi Company, their locations, systems and
power are shown in the following table :
Fig. 322 — Bank of High Voltage Transformers
at Kahuku.
Location
Carnarvon,
Wales
System
Continuous and discontinuous
waves
Power
100-300 K.W.
Wave Length
in Meters
6,000 to 10,000
Clifden,
Ireland
Discontinuous waves
75-150 K.W.
5,500
Glace Bay,
Nova Scotia
Discontinuous waves
75-150 K.W.
8,000
Stavanger,
Norway
Continuous waves
150 K.W.
p
Marion, Mass.
Continuous waves
150 K.W.
?
New Brunswick,
New Jersey
Continuous and discontinuous
waves
150-300 K.W.
8,000 to
15,000
Bolinas,
California
Kahuku, Hawaii
Discontinuous waves
Discontinuous waves
Discontinuous
300 K.W.
300 K.W.
. 300 K.W.
6,000 to
6,000 to
6,000 to
10,000
12,000
12,000
Location
Sayville,
Long Island
Tuckerton,
New Jersey
MARCONI TRANSOCEANIC RADIO TELEGRAPHY. 307
OTHER TRANSOCEANIC STATIONS.
System Power Wave Length
Joly-Arco (continuous waves) 100 K.W. 9,400 meters
Goldschmidt High Frequency
Alternator (continuous waves)
7,400 meters
arc
Fig. 323— U. S. Naval Radio Station at Radio, Va. (Arlington).
APPENDIX
SECTION A.
COMPLETE DATA FOR STANDARD MARINE COMMERCIAL SETS.
Transformer
Voltage
Capacity High
Voltage Con-
Antenna Current
(Average)
Type
Power Rating
Primary
Secondary denser (mfds.)
600 met. 450 met. 300 met.
P-4
2
K.W.
500
cycle
350-140
12,500
.012 (600 met.)
12 to 17 amp.
9-13 3
to 5
.006 (300 met.)
P-5 *
>
K.W.
500
cycle
350-120
14,500
.004
5^
to 8
5-72
to 4/
E-2 J
j
K.W.
120
cycle
300-110
14,700
.01
5 to
7
ll/2
to 3
Composite
1
K.W.
60
cycle
110
18,000
.008
5 to
7
!/>
to 3
Composite
2
K.W.
240
cycle
500
15,000
.008
5/2
to 8
1/2
to 3
P-9 }
I
K.W.
500
cycle
300-110
15,000
.002
3 to
4
1
to 2
The foregoing data will familiarize the student with the .power rating, electrical dimen-
sions of the oscillation circuits, voltages, current, etc., of the various transmitters of the
American Marconi Company, knowledge of which is essential to the practical operator.
SECTION B.
WAVE LENGTH RANGE OF MARCONI RECEIVING TUNERS.
Type 101 200 to 7,500 meters
Type 107a 300 to 2,500 meters
Type 106 200 to 3,500 meters
Type 112 200 to 2,500 meters
.0
.05
.1
.2
.3
.4
.5
.6
.7
.8
.9
1.0
SECTION C.
CORRECTION FACTOR FOR FORMULA.
. 27T
Wave length = — X 9.5 X V L C7
K
La
Values of K corresponding to —
Li
Where L? = inductance of loading coil at base,
LA = distributed inductance of antenna.
K
1.57
1.51
1.426
1.314
1,219
1.142
1.078
1.022
.968
.925
.892
,855
1.5
2.
2.5
3.
4.
5.
6.
7.
8.
9.
10.
K
.735
.65
.59
.545
.475
.430
.40
.370
.350
.325
.31
APPENDIX. 309
SECTION D.
1NDUCTIVITY VALUES FOR DIFFERENT DIELECTRICS.
Dielectric. Inductivity Value, "K"
Flint Glass, Double Extra Dense 10.10
Flint Glass, Very Dense 7.40
Flint Glass, Light 6.85
Mint Glass, Very Light 6.57
Castor Oil 4.80
Quartz 4.50
Porcelain 4.38
Mica Sheet, Pure 4.00 to 8.00
Glass, Common (Radio-Frequency) 4.21
Glass, Common (Low Frequency) 3.25 to 4.00
Sperm Oil 3.02 to 3.09
Olive and Neats-Foot Oils 3.00 to 3.16
Shellac 2.74 to 3.60
Gutta Percha 2.46 to 4.20
Sulphur 2.24 to 3.84
India Rubber, Pure 2.22 to 2.497
Turpentine 2.15 to 2.43
Hard Rubber Ebonite 2.05 to 3.15
Petroleum 2.03 to 2.42
Resin 1.77 to 2.55
Paraffined Paper 3.65
Paraffine Wax v 1.9936 to 2.32
Beeswax 1.86
Paraffine, Clear 1.68 to 2.32
Celluloid 1.555
Manila Paper 1.50
Air at Ordinary Pressure, Standard 1.0000
SECTION E.
Conversion of X = — to X = 59.6 V L C
N
If L be expressed in henries, C in farads, R in ohms, and N in cycles per second, Ohm's law
for alternating current is expressed,
T
27rNC
1
Where 2?rNL— — = is the expression for the reactance of a circuit containing induc-
tance and capacity.
1 E
If 2^r N L = - - we have resonance and therefore I = — (See paragraphs 45 and 46).
27r NC R
If in any given oscillation circuit,
2?r N L = then, evaluating,
47r2 N2 L C = 1
1
hence, N' =
310 PRACTICAL WIRELESS TELEGRAPHY.
which is the fundamental equation for the frequency of an oscillation circuit. As shown in
paragraph 91, if X, the wave length, be expressed in meters, N in cycles per second and V
the velocity of electrical waves = 300,000,000 meters per second, then
300,000,000
X—
N
1
But N=
27T V L C
300,000,000
hence X = — : = 300,000,000 X 2*r X V L C
1
27rV LC
The microhenry and the microfarad are more convenient units for practical oscillation cir-
cuits. Also 1 farad = 1,000,000 microfarads, and 1 henry = 1,000,000 microhenries. Hence,
if the inductance and capacity are to be expressed in such units we must divide L and C
by 1,000,000, then
J_
T -1 C\C\C\ AAA 1 AAA AAA
=2* X 300,000,000 X
1,000,000 1,000,000
If we take 1,000,000 out from under the radical,
300,000,000
V L C = 2*- x 300 X V L C
1,000,000
If L be expressed in centimeters and 1 microhenry = 1,000 centimeters, then we must
divide L by 1,000, hence,
X = 2*- X 300 X
1,000
Taking out 1,000 under the radical (and since V 1,000 = .31.62)
6.2832 X 300
X = X V L C
31.62 .
or X = 59.6 VlTC
SECTION F.
The following scries of questions bear directly and indirectly on the tc.vt of this volume,
and are considered as a representative set for training students to become wireless operators.
They were intended primarily to guide the instructor in outlining a complete instruction
course, but will be valuable to the elementary student of radio as well.
PART I.
Magnetism.
Ques. (1) Describe a permanent magnet.
Ques. (2) Name the metals subject to magnetic influence.
Ques. (3) Show by diagram the resultant magnetic field between two north poles in proximity.
Ques. (4) Draw a diagram showing the resultant magnetic field between a north and south pole.
Ques. (5) What is meant by the earth's magnetism?
Ques. (6) Where is the north magnetic pole located?
Ques. (7) What is the behavior of soft iron and hard steel under the influence of a magnetizing
force?
Ques. (8) Can all bodies be magnetized?
Ques. (9) What is said to be the direction of the lines of force in a magnet?
APPENDIX.
311
PART II.
Elementary Electricity and Simple Circuits.
Ques. (1) What is meant by a "positive" and a "negative" charge of electricity?
Ques. (2) Explain the application of the term "electromotive force" to an electrical circuit?
Ques. (3) Name four methods by which an electromotive force can be generated.
Ques. (4) Explain briefly the actions taking place within an ordinary chemical electrical cell.
Ques. (5) Show by diagram a series connection of electrical cells.
Ques. (6) Show by diagram a parallel connection of electrical cells; a series parallel connection.
Ques. (7) Define the term resistance as applied to an electrical circuit.
Ques. (8) What is meant by an open circuit; a short circuit; a closed circuit?
Ques. (9) What is the unit for current pressure; current strength; resistance.
Ques. (10) Explain Ohm's law and apply it to an electrical circuit; work out a simple problem.
Ques. (11) How is the power of a direct current measured?
Ques. (12) Work out a simple problem showing the joint resistance of three resistances of different
values connected in parallel.
Ques. (13) Define a volt, ampere, ohm, watt and give the standard value of each.
Ques. (14) What metals offer the greatest resistance to the flow of an electrical current?
Ques. (15) Will pure water conduct electricity?
Ques. (16) Will impure and salt water conduct electricity?
Ques. (17) The voltage of a circuit in 100 volts; the resistance 10 ohms; what will be the
strength of the current when the circuit is closed?
Ques. (18) How many amperes will a 100 watt Tungsten lamp draw on a 120 volt circuit?
Ques. (19) What power is consumed in applying a current at pressure of 220 volts to a circuit
the resistance of which is 20 amperes?
PART III.
Electromagnetism — Electromagnetic Induction — Electrical Measuring Instruments — The
Flow of Alternating Current.
Ques. (1) Describe the essentials of an electromagnet.
Show by diagram the direction of the lines of force about a solenoid.
Show by diagram the direction of the lines of force about the poles of a horse-shoe
Ques. (2)
Ques. (3)
magnet.
Ques. (4)
regulated?
Ques. (5)
Ques. (6)
How may the strength of the magnet field about the poles of an electromagnet be
Show by diagram the principle of electromagnetic induction.
Explain the terms self-induction; mutual induction.
Ques. (7) Draw a circuit diagram of an induction coil with a magnetic interrupter and explain
fully its operation.
Ques. (8) Show by diagram a step-up transformer; a step-down transformer; an auto transformer;
an air core transformer.
Ques. (9) Show by diagram the construction and working of a galvanometer; a voltmeter; an
ammeter; a wattmeter.
Ques. (10) Explain the use of a shunt in connection with an ammeter.
Ques. (11) Explain briefly how current is generated in a dynamo.
Ques. (12) Draw a diagram of a shunt-wound dynamo; a series-wound dynamo; a compound-wound
dynamo.
Ques. (13) Show by diagram the differences in construction between a ring-wound armature and
a drum-wound armature.
Ques. (14) How can the voltage of a dynamo be increased or decreased?
Ques. (15) What effect has an increase of the speed of the armature on the voltage of a dynamo.
Ques. (16) Show by diagram the construction of a field rheostat.
Ques. (17) Explain by diagram the function of a commutator in a dynamo; similarly the function
of the collector rings.
Ques. (18) Explain briefly how an electric motor operates.
Ques. (19) State two methods by which the speed of a motor can be increased.
Ques. (20) Show the circuits of a differentially compound-wound motor.
Ques. (21) How may the frequency of a generator be increased?
Ques. (22) What is the frequency, in cycles per second, of the generators used in commercial
wireless telegraphy?
Ques. (23) What effect has a series condenser on the flow of alternating current; the effect
of a series inductance.
Ques. (24) What is meant by a resonant circuit?
Ques. (25) Give Ohm's law for alternating current (See Appendix).
Ques. (26) Explain the meaning of the term "power factor."
Ques. (27) How is the power of an alternating current measured?
Ques. (28) Show by diagram two practical electrical circuits.
Ques. (29) Explain how a fuse operates.
Ques. (30) What is meant by the effective value of an alternating current?
Ques. (31) How is the power output of a generator increased? Decreased?
Ques. (32) What is meant by a separately excited dynamo?
312
PRACTICAL WIRELESS TELEGRAPHY.
Ques. (33) How can you reduce the output of an alternating current dynamo without reducing
the frequency?
Ques. (34) What is the frequency of a 30 pole generator revolving at a speed of 2,000 revolutions
per minute?
Ques. (35) Define the terms cycle, frequency and amplitude.
Ques. (36) Show by diagram the difference between a step-up voltage transformer and a step-
down voltage transformer.
PART IV.
Motor Generators and an Automatic Motor Starter.
Ques. (1) Draw a diagram of a motor generator consisting of a differentially-wound motor and
a simple shunt-wound generator.
Ques. (2) Draw a circuit diagram of a simple shunt-wound motor generator.
Ques. (3) Explain by diagram the Cutler Hammer type of motor starter; similarly the General
Electric Company's hand starter.
Ques. (4) Give a complete circuit diagram of the automatic starter used in connection with the
Marconi 2 K. W. 500 cycle panel set.
Ques. (5) Give a circuit diagram of a Y2 K. W. automatic starter used in connection with the */z
K. W. 500 cycle Marconi panel set.
Ques. (6) Show the use of protective condensers on a motoc generator; also protective resist-
ance rods.
Ques. (7) How often must the bearings of a motor generator be oiled?
Ques. (8) How would you clean the commutator of a motor?
Ques. (9) How would you clean the brushes of a motor?
Ques. (10) Show how to locate an open coil in a motor amature.
Ques. (11) How would you locate a short circuit in one of the field coils of the motor generator?
Ques. (12) How would you detect a "ground" in the circuits of a motor generator?
Ques. (13) How would you know that the motor generator is running at normal speed?
Ques. (14) How would you repair a burned-out resistance coil in a motor starter?
Show how to repair a burned-out field rheostat,
Why are high frequency generators used in wireless telegraphy?
Ques. (15)
Ques. (16)
Ques. (17) Explain two different methods of controlling the speed of a motor?
Ques. (18) Why cannot the starting box be used as a speed controller?
Ques. (19) Why is a motor generator necessary for a wireless set?
Ques. (20) State several causes for a generator failing to generate while the motor is running.
Ques. (21) What effect has an increase of the speed of a motor generator?
PART V.
Storage Batteries.
Ques. (1) Describe the points of difference between the lead-plate storage cell and the nickel—
iron-alkali storage cell.
Ques. (2) What is the fully charged and discharge voltage of each?
Ques. (3) Explain the use of a hydrometer?
Ques. (4) How often should a storage cell be placed on charge?
Ques. (5) What care is necessary from day to day to keep storage cells in first class condition?
Ques. (6) How can you locate an open circuit in a storage cell battery?
Ques. (7) What is the normal charging rate of a storage cell?
Ques. (8) What is the normal discharge rate of a storage cell?
Ques. (9) Explain the use of an overload circuit breaker in the charging circuit of a storage
battery?
Ques. (10) Explain thoroughly the use of an underload circuit breaker in a storage battery
charging circuit.
Ques. (11) Describe and explain the use of the amperehour meter.
Ques. (12) What causes sulphating and buckling of storage cell plates and how many it be
prevented?
Ques. (13) State at least two methods by which the amount of charge of a storage battery may
be determined?
Ques. (14) What is the essential difference between a primary and a storage battery?
Ques./ (15) What will be the effect if a lead cell is discharged too rapidly; overcharged or
charged in the wrong direction?
PART VI.
Condensers, Oscillation Generators and Radio Transmitters.
Ques. (1) Define and describe the construction of a condenser.
Ques. (2) Describe three types of high-voltage condensers.
Ques. (3) Explain the points of difference in construction between a high-voltage and a low-
voltage condenser.
Ques. (4) Draw a diagram showing a number of condensers connected in series; in parallel.
Ques. (5) If a condenser of .002 microfarads and another of .005 microfarads are connected in
series, what is the resultant value of capacity?
Ques. (6) What is the capacity of a standard Marconi Leyden jar?
APPENDIX.
313
Ques. (7) Describe fully what takes place when a condenser discharges across a spark gap
through a coil of wire.
Ques. (8) What is meant by the "time period" of an oscillation circuit?
Ques. (9) What are radio-frequent electrical oscillations?
Ques. (10) Explain the term "wave length" as applied to an oscillation circuit.
Ques. (11) If the capacity of the condenser in a closed oscillation circuit be increased, what
effect has such increase upon the wave length?
Ques. (12) What effect has an increase of inductance in an oscillation circuit?
Ques. (13) Draw a diagram of an open oscillation or radiating circuit, and describe briefly the
use of the apparatus included therein.
Ques. (14) How may an aerial be turned to radiate a wave longer than the natural or funda-
mental wave; how can it be tuned to radiate a wave shorter than the natural wave?
Ques. (15) Show by diagram four methods for setting an antenna into electrical oscillation.
Ques. (16) Show by diagram the distinction between damped and undamped oscillations.
Ques. (17) What is meant by the logarithmic decrement of the antenna oscillations?
Ques. (18) What is the purpose of a short wave condenser in a transmitting system?
Ques. (19) How can you tell if the condensers in the closed oscillation circuit of a transmitter
are punctured?
Ques. (20) Explain the changes necessary to reduce the wave radiated by a transmitting set
from 600 to 300 meters.
Ques. (21) Draw a complete fundamental circuit diagram of a radio transmitting set, and explain
briefly the function of each part of the equipment.
Ques. (22) How are electromagnetic waves produced?
Ques. (23) Define the term resonance as applied to wireless telegraph circuits.
Ques. (24) How are two circuits placed in resonance?
Ques. (25) What is meant by the term spark frequency and upon what does the pitch or the
tone of the spark depend?
Ques. (26) Define the term damping and show by diagram the apparatus that produces damped
oscillations.
Ques. (27) Define a sharp wave; a pure wave; what is meant by the term broad wave?
Ques. (28) Are broad waves caused by highly damped or by slightly damped oscillations?
Ques. (29) How does coupling effect the sharpness of the wave?
Ques. (30) What is meant by the electrical length of a conductor in radio?
Ques. (31) Why are transformers used instead of induction coils in transmitting sets?
^ Ques. (32) Which is the most efficient transmitting set, a conductively or inductively coupled set?
PART VII.
Appliances for the Radio Transmitter.
Ques. (1) Name and describe four types of spark dischargers employed in radio telegraphy.
Ques. (2) State the advantages and disadvantages of each type.
Ques. (3) Suppose a secondary section of a high voltage transformer should burn out, how would
you make a temporary repair?
Ques. (4) What are the essential points of difference in the construction of an open core and a
closed core transformer?
Ques. (5) Give a detailed sketch showing the construction of an open core transformer.
Ques. (6) How would you synchronize a rotary spark gap?
Ques. (7) Describe the construction of a quenched gap.
Ques. (8) Describe a primary reactance coil and explain its use.
Ques. (9) Why is the short wave condenser of a transmitting set composed of several condenser
jars connected in series?
Ques. (10) Show how the coupling of a transmitting set can be varied by means of a variometer?
PART VIII.
Aerials or Antennae.
Ques. (1) Draw a diagram of a flat top aerial; an umbrella aerial; a "T" aerial; a vertical aerial.
Ques. (2) Which of the four types is the most advantageous for commercial wireless telegraph
working?
Ques. (3) At what point must the antenna or aerial wires be well insulated?
Ques. (4) What care is necessary to keep a ship's aerial in first class shape?
Ques. (5) How many wires are used in the usual Marconi ship aerial?
Ques. (6) Show by diagram a test for determining if the antenna insulators are leaking.
Ques. (7) How would you temporarily repair a leaking insulator?
Ques. (8) What is the natural wave length of the average ship's aerial?
Ques. (9) What is the capacity in microfarads of the average ship's aerial?
Ques. (10) What is the inductance in centimeters of the average ship's aerial?
Ques. (11) Can an aerial which has a natural wave length of 600 meters be operated at the
wave length of 300 meters?
Ques. (12) What is the effect of increasing the number of wires of an antenna?
Ques. (13) How -may an aerial be adjusted to radiate a sharp wave?
Ques. (14) How would you adjust an aerial, the natural wave length of which was 525 meters,
to radiate a wave of 300 meters?
314 PRACTICAL WIRELESS TELEGRAPHY.
PART IX.
Receiving Apparatus.
Ques. (1) Draw a fundamental circuit diagram of an inductively coupled receiving transformer?
Ques. (2) Draw a diagram of the direct coupled receiving transformer.
Ques. (3) Show by diagram the circuit best suited to the carborundum detector.
Ques. (4) Draw a wiring diagram of a tuner suitable for the Marconi magnetic detector.
Ques. (5) Draw a diagram showing the construction of the Marconi magnetic detector, and explain
its operation.
Ques. (6) Draw a circuit diagram of the tuning circuits for the Fleming valve detector; also
for the Marconi multiple tuner.
Ques. (7) Show by diagram and explain fully how a telephone receiver operates.
Ques. (8) What is the use of a potentiometer in a receiving set?
Ques. (9) How would you adjust a receiving tuner for ''broad" tuning?
Ques. (10) How would you adjust a receiving tuner for "sharp" tuning?
Ques. (11) Show by diagram how you would locate an open circuit in the coils of a receiving
tuner.
Ques. (12) Show by diagram how you would locate a short circuit in a variable condenser.
Ques. (13) What is the use of the variable condenser in shunt to the secondary winding of a
receiving transformer?
Ques. (14) What is the function of the fixed condenser in a receiving set?
Ques. (15) How would you adjust a carborundum detector to its maximum degree of sensitive-
ness?
Ques. (16) Explain a buzzer tester and how it operates.
Ques. (17) How could a receiving set be calibrated with a wavemeter?
Ques. (18) Explain the use of an aerial changeover switch.
Ques. (19) How do you protect the receiving apparatus from lightning discharges?
Ques. (20) Describe a variable condenser and its effect on the various circuits of a receiving set.
Ques. (21) What is the function of a crystalline detector in receiving signals?
Ques. (22) Why are high resistance telephones used in receiving sets?
Ques. (23) How do you protect a crystalline detector from the local transmitter?
Ques. (24) Show by diagram a test buzzer and its uses.
Ques. (25) Why should the coupling be reduced, when receiving, to the point where the signals
are just readable?
Ques. (26) Show how the primary and secondary circuits of a receiving tuner are adjustFll to
resonance?
Ques. (27) Show how the coupling may be decreased with a conductively coupled receiving set?
Ques. (28) Show by diagram the simplest possible apparatus for the reception of signals?
PART X.
Emergency Apparatus and Auxiliary Transmitters.
Ques. (1) Draw a fundamental diagram of the Marconi ten-inch coil auxiliary set.
Ques. (2) Draw a circuit diagram showing the charge and discharge circuits of a 60 cell storage
battery of the type employed in connection with the 2 K. W. 500 cycle motor generator.
Ques. (3) When would you make use of the auxiliary transmitter?
Ques. (4) What is the maximum distance which an auxiliary set must be capable of transmitting
according to the United States regulations?
Ques. (5) Draw a complete circuit diagram of the Electric Storage Battery Company's charging
panel.
PART XL
Practical Radio Measurements.
Ques. (1) Explain fully by diagram the method of tuning a transmitting set to the standard
international waves.
Ques. (2) Show by diagram a test for determining the purity or sharpness of the radiated waves.
Ques. (3) Show by diagram and explain the method of tuning a transmitting set to resonance by
an aerial ammeter.
Ques. (4) Show by diagram and explain how a receiving set can be tuned to a standard wave
length.
Ques. (5) Show by diagram and explain the method of measuring th« logarithmic decrement of
a group of oscillations.
Ques. (6) Calculate the inductance of a coil of wire 12 inches in length, 3% inches in diameter
wound closely with No. 28 S. S. C. wire.
Ques. (7) Explain the apparatus for and the method of plotting a resonance curve.
PART XII.
Marconi Transmitters.
Ques. (1) Draw a circuit diagram showing the circuits of radio-frequency for the Marconi 2 K.
W. 500 cycle panel set.
Ques. (2) How would you adjust the quenched spark transmitter of this set for a clear note and
maximum flow of antenna current?
APPENDIX. 315
Ques. (3) Explain the functioning of the wave-length changing switch in the Marconi 2 K. W.
500 cycle set.
Ques. (4) State the condenser capacity of the 2 K. W. 500 cycle panel set; the ^ K. W. 500
cycle panel set; the 1 K. W. 60 cycle composite set.
Ques. (5) How do you change from the quenched spark gap to the rotary gap in the new panel
sets?
Ques. (6) How do you adjust the acceleration of the starter arm on the automatic starter?
Ques. (7) If upon closing the starting switch, the automatic starter failed to work, where would
you look for the trouble?
Ques. (8) Explain fully the steps necessary to tune the 2 K. W. panel transmitter for the maxi-
mum flow of antenna current at the three standard waves.
Ques. (9) How do you change the length of the radiated wave on the panel transmitter?
Ques. (10) How would you synchronize a rotary spark gap of a Marconi set and adjust it for
clear tones?
Ques. (11) How may the power input of the panel sets be reduced?
Ques. (12) State fully the steps necessary to disassemble a quenched spark gap, clean it and put
it together again.
PART XIII.
Marconi Direction Finder.
Ques. (1) Show the fundamental circuits of the Marconi direction finder complete.
Ques. (2) Show how the position of a radio station may be located.
Ques. (3) How may the direction finder circuits be preadjusted to standard wave lengths?
Ques. (4) Explain how the direction finder is tuned to a transmitter.
PART XIV.
Undamped Oscillation Generators.
Ques. (1) Show by diagram the circuits of the arc generator.
Ques. (2) How are continuous waves generated?
Ques. (3) Show by diagram the difference between continuous and discontinuous waves.
Ques. (4) Describe briefly the principle of the Goldschmidt alternator.
Ques. (5) Explain by diagram the system for increasing the frequency of a radio-frequency alter-
nator, by means of transformers.
PART XV.
Receivers of Undamped Oscillations.
Ques. (1) How can undamped oscillations be made audible at the receiving station?
Ques. (2) Explain the operation of the tikker, the heterodyne and the regenerative beat receiver,
Ques. (3) Describe Marconi's method for making undamped oscillations audible with a crystal
rectifier detector.
LOCATION OF TROUBLE.
The questions herewith presented do not bear directly upon the text in this volume.
It is expected that they will be used by the Instructor in charge who will explain the
various methods of locating trouble in detail.
Ques. (1) If the storage cells of a radio set gas violently while charging, what is the cause?
Ques. (2) If the hydrometer indicates that the specific gravity of a storage cell is too low (when
the cell has been fully charged), how would you proceed to bring gravity up to normal.
Ques. (3) If one cell of a storage battery unit did not show full voltage, how would you proceed
to bring it to normal voltage?
Ques. (4) How would you remedy sparking at the brushes of a motor?
Ques. (5) If the motor refused to start, what might be the cause of the trouble?
Ques. (6) If the release magnet of a starting box burned out, how would you keep the motor
in running order?
Ques. (7) If one or more of the resistance coils of a starting box burned out, how could the
motor be started?
Ques. (8) Show by diagram a method of constructing a salt water rheostat for temporary use.
Ques. (9) Show how a bank of lights may be used for the same purpose?
Ques. (10) How many lamps would be required in a circuit (as a lamp bank resistance) to allow 30
amperes to pass?
Ques. (11) If a dynamo refused to generate, what might be the trouble?
Ques. (12) Show by diagram a test to determine trouble in either the primary or secondary wind-
ings of a transformer?
Ques. (13) If the spark of a radio transmitter discharges irregularly, what might be the cause of
the trouble?
Ques. (14) What is the effect if the spark gap of a transmitter is opened too wide?
Ques. (15) If an entire bank of high voltage condensers should puncture, how would you manage
to maintain communication?
Ques. (16) What would be the effect if the synchronous rotary spark gap accidently gets out of
synchronism? .
316 PRACTICAL WIRELESS TELEGRAPHY.
Ques. (17) If one of the condensers in a transmitting set breaks down, what would you do to
place it in working order?
Ques. (18) How may a receiving tuner be adjusted to decrease the effects of static?
Ques. (19) How would you test for an open circuit in the coils of a receiving tuner?
Ques. (20) If a telephone tests open when the tips of the cords are connected to the terminals of
a battery, what might be the trouble and how can you remedy it?
Ques. (21) If during the reception of signals they weaken with the roll of the ship, what might
be the trouble and how can it be remedied?
Ques. (22) If your antenna blew down at sea so that only a portion of the wire remained, how
would you rig up the transmitting apparatus for communication?
Ques. (23) Show by diagram a test for determining a leak in the antenna circuit. Show the
connections for this test and name one remedy for it.
INTERNATIONAL REGULATIONS AND U. S. LAWS AND REGULATIONS
(Prepared by H. Chadwick.)
Ques. (1) What is the International Distress signal?
Ques. (2) What is the distance requirement for auxiliary apparatus?
Ques. (3) Are you compelled to exchange wireless telegraph traffic with ships and Stations
regardless of the system used?
Ques. (4) State the law regarding the use of unnecessary power.
Ques. (5) What is the rule in regard to the disposal of traffic through the nearest coast station?
Ques. (6) Has the sender of a message the right to designate the routing of his message?
Ques. (7) What are the penalties for violations of the U. S. Radio Laws?
Ques. (8) What are the international normal wave lengths for a ship station?
Ques. (9) What other wave lengths may be used by ship stations and when?
Ques. (10) What wave lengths are standard for commercial radio traffic?
Ques. (11) What shall the charge for radiograms comprise?
Ques. (12) May operating practice be indulged in aboard ship?
Ques. (13) What is the international regulation regarding the use of superfluous signals?
Ques. (14) What is the U. S. law in regard to the secrecy of messages?
Ques. (15) What are the U. S. requirements for an auxiliary equipment; also the international
requirements?
Ques. (16) From whom are charges for radiograms generally collected? State exceptions.
Ques. (17) What code of signals is used for wireless telegraph communication?
Ques. (18) Does the coast or ship station determine the order of working?
Ques. (19) By what method would you call a station?
Ques. (20) When would you use the "CQ" call?
Ques. (21) After calling a station three times without result, how long must you wait before
repeating a call?
Ques. (22) Give the following signals:
(a) The attention signal.
(b) The termination of a message.
(c) The "go ahead" signal.
Ques. (23) What is the rule in regard to the transmission of long messages?
Ques. (24) According to the International Regulations how often may a message be repeated
before being cancelled?
Ques. (25) What signal designates the conclusion of correspondence?
Ques. (26) Give as many of the International abbreviations as possible.
SECTION G.
THE RELATION OF 'SPARK GAP ACTION TO COUPLING AND PURITY
OF THE RADIATED WAVE.
Frequently much confusion arises in the mind of the radio student as to the existence
and cause of two waves being radiated by a wireless telegraph transmitter. It should
be understood that a transmitter in proper adjustment for practical use never radiates
a double wave, but in fact should always radiate a single wave, of wave length and damp-
ing normal to the antenna circuit as adjusted, but with any transmitter two waves will
appear if the spark gap is not in proper condition. The remedy in event of the latter is
to restore the gap to its proper working qualities or to loosen the coupling at the oscilla-
tion transformer.
When the spark discharges across the gap it acts as a trigger to start the primary
circuit into oscillation and the stored energy of the condenser will be transferred to the
antenna circuit until in the course of a few oscillations (the number decreasing as the
coupling is closer), the voltage in the primary circuit becomes so low that the spark will
APPENDIX. 317
no longer discharge across the gap; the primary oscillations will then cease. The exact
value of the minimum voltage for non-sparking will depend upon the resistance of the
gap.
The resistance of the spark gap always increases as the oscillating current decreases
and if it were not for the burnt gases which exist in the immediate vicinity of the dis-
charge gap, the original resistance would be restored at the end of the first half oscilla-
tion. Since there is a lag in the cooling and dissipation of the hot gases, this does not
occur, but if the gap is properly cooled, that is the electrodes do not get too hot, the
resistance becomes so high after a few oscillations that the reduced voltage of the con-
denser cannot maintain the spark. In other words, the spark is quenched and the oscilla-
tions of the two circuits will take the form shown in Fig. 118, that is, after a few swings
of the primary circuit, the primary oscillations will cease and the antenna circuit will
oscillate at its natural frequency and decrement.
These are the precise actions taking place in a properly adjusted radio transmitter,
no matter what type of spark gap is employed, if the electrodes are clean and smooth,
the ventilation adequate and the coupling of the oscillation transformer is not too close.
The rate at which the gases in the gap are dissipated or the non-conducting qualities
of the gap restored, determines how close the coupling can be made without interfering
with the quenching of the spark. If the coupling is so close that the reaction of the
secondary upon the primary not only does not extinguish the spark but transfers energy
back to the primary then the spark will not be quenched until the energy of the entire
system has fallen to a low enough value to allow the high resistance of the gap to be
restored. The complex oscillations shown in Fig. 109 will then result and the effect of
two waves radiated will be produced. If the spark quenches after one or two of the
"beats" shown in Fig. 109 and the antenna still has energy to be radiated, then investiga-
tion with a wave meter may show three apparently different wave lengths radiated.
. In all spark gaps there is a tendency toward "arcing," that is, for the spark to be fol-
lowed by passage of the power current across the gap. This will prevent the restoration
of the high resistance — the spark will not quench.
The plain open spark gap without artificial means of cooling requires very careful
adjustment and reduction of coupling to give proper operation, that is freedom from
double wave emission. Unless the spark voltage is carefully adjusted the tendency
toward arcing is difficult to control and the action tends to be irregular. The use of
special cooling means, such as a series of gaps or an air blast enables good quenching to
be obtained with sufficient regularity to give a clear spark tone.
The improved forms of spark gap, such as the rotary and so-called "quenched gap"
(i. e. multiple plate gap) have the advantage of giving good quenching with a tighter
coupling and hence a smaller number of oscillations in the primary circuit. This, of
course, means higher efficiency and greater antenna current for a given input because
less energy is lost in heat in the primary circuit.
With equal perfection of apparatus there is little to choose between these gaps so far
as tightness of coupling without failure to quench is concerned, as is evidenced by the
recent Marconi sets which are provided with both forms of gap.
If either of these gaps gets into bad condition, or becomes overheated, double waves
will be radiated, showing that the spark has ceased to be extinguished after the energy
has been transferred to the antenna. This can only be remedied by restoring the gap
to normal condition or loosening the coupling. If the gap is in particularly bad condi-
tion, loosening the coupling will not prove effective.
Proper adjustment of the spark gap is very difficult to obtain unless the power supply
circuit is properly designed. It may be said that no form of spark gap will quench reli-
ably if the source of current supply is effectively short circuited by the spark. The
power circuit must have sufficient inductance or resistance so that the voltage applied to
the condenser will fall when the spark passes, otherwise arcing will be produced, quench-
ing will not take place and a complex wave emission will result.
SECTION H
IMPORTANT REMARKS ON THE DESIGN, ADJUSTMENT AND USE OF
1 RECEIVING TRANSFORMERS.
According to the grade of service for which it is employed, the receiving oscillation
transformer may have either a secondary coil with a fixed number of turns, without a shunted
318 PRACTICAL WIRELESS TELEGRAPHY.
condenser ; a secondary having a variable number of turns, without a shunted condenser ; or
either type of secondary with a shunted variable condenser. In practically all types of
transforr-iers, variable coupling between the primary and secondary is provided.
The most efficient secondary circuit is probably the simple non-variable coil, minus a
shunt variable condenser, provided the coil is so constructed, that, with detector, stopping
condenser and telephones connected, it's natural period of oscillation is that of the signal
being received.
Such a circuit has often been called an untuned circuit, meaning that it does not possess a
frequency varying condenser or inductance. By some this has been assumed to mean a non-
oscillatory circuit and the high resistance of the detector has been stated to be the reason
for so calling it. The error of this view has often been pointed out and Kolster has shown
(proceedings Institute Radio Engineers, Vol. 1, page 25) that such a circuit gives a perfectly
normal resonance curve of fairly small decrement and hence is oscillatory and resonant to a
particular frequency.
If resonance curves of such a circuit be taken, it will be found that the behavior of
the circuit varies with the coupling and with the setting of the detector. For a given
adjustment of the crystal, the shape of the resonance curve, and the location of the maximum
point will vary with the coupling. The curve is broader for close coupling.
If resonance curves be taken for a fixed loose coupling, but with a number of different
crystal settings, it will be found that the highest points in the curves do not coincide, but
occur at different wave lengths for different crystal adjustments and that the curves will
also differ in shape, some being sharp and others broad.
The reasons why such a circuit is oscillatory is that the coil has distributed capacity
which is equivalent to a condenser shunted across the inductance. This capacity is increased
by the capacity of the connected elements. The reason w,hy it is resonant is that its
inductance and capacity are made such that its natural time period is the same as that of the
signal to be received. A small shunted capacity tends to impress a high potential on the
detector for a given amount of received energy and hence a loud signal is obtained. As its
capacity can be made quite small, such a simple non-variable coil secondary is found to be a
very efficient receiver when it's time period agrees with that of the signal to be received.
By varying the coupling and the crystal adjustment, therefore, such a circuit can be made
to tune broadly or fairly sharply and be put in resonance for waves varying over a sufficient
range of wave length to meet the needs of a certain class of service.
For the reception of signals over a wider range of wave lengths, the use of coils having
a variable number of turns enables the natural period of the secondary circuit to be adjusted
to cover such range by varying the number of turns. A coil of variable inductance,
however, may be less efficient owing to the possible consumption of energy due to the flow of
oscillations in the unused turns.
Where efficient reception and also high selectivity is required over a large range of wave
lengths, as, for example, from 300 to 3,000 meters, a coil having a variable number of turns
and a shunted variable condenser is employed. The loudest signals would usually be obtained
with such a receiver by either disconnecting the condenser or using it at a small value of
capacity and properly adjusting the coupling, a moderately close (but not the closest)
coupling being employed. Where, however, there is trouble from interference, better recep-
tion will be had by further loosening the coupling, reducing the inductance and increasing the
capacity of the shunted condenser. By this means, with an efficient detector, signals of very
small difference in wave lengths may be separated or "tuned out."
For best results, however, the maximum capacity of the shunted variable secondary
condenser should not be large and it's minimum or "zero" capacity should be as small as
possible.
The effect of the "over-hanging" or unused turns may be minimized by disconnecting such
turns from the used portion and this is the purpose and function of the "end turn switches"
with which the most complete present-day receivers are provided, as described in Chapter 9.
SECTION I.
The correct phase relation between the currents of the main receiving aerial and the
balancing out aerial in Marconi Duplex System is obtained by grounding the balancing
aerial at the end nearest to the local transmitter, the coupling coil (for the balancing aerial)
being connected in the circuit at a considerable distance from the earthed end.
INDEX
Page
AERIALS 116
advantages or disadvantages, various types
of 121
Bellini-Tosi 123
Bradfield insulator for 124
change-over switch for 114, 115
deck insulator for 123, 124
directional 121
"dummy" 127
effective inductance and capacity, measure-
ment of 214
flat top 119
for direction finder 256
function of 116
function of receiving 129, 130
fundamental considerations, in design of.. 118
fundamental wave length of "T" 119, 120
induction of current in direction finder.... 258
installation of ship's 124
inverted "L" type 119
loading inductance for 117
standard Marconi ship 123
table of wave lengths of 121
"T" type 119
tuning elements for receiving 130
tuning inductance for 109
umbrella 119
vertical 118
wave length of 117
Alexanderson Alternator 268
Alternating Current
effective value of i 41
lag and lead of ." 40
Alternating Current Dynamo 26
Alternator 22, 23
Alexanderson, high frequency 268
diagram of, fundamental 25
Goldschmidt radio frequency 270, 271
Ammeter 43
hot wire 45
thermo 46
with shunt 43
Ampere hour
meter for measurement of 72
unit as applied to storage cells 70
Amplifier
microphonic 169, 170
radio-frequency 163, 164, 284
telephone 167, 168
vacuum valve 163
Antenna
decrement of 126
definition of 87
Arc Transmitters 265, 266
Navy type 266
signalling with 267
Armatures
drum 31
dynamo 31
motor 31, 32
ring 31
Armature Windings 31
construction of 56
development of 31, 32
lap 32
wave 33
ring 3.1
Atmospheric Electricity 171
Audibility Meter 217
Auxiliary Transmitters 179
adjustment of 180, 181
Marconi type 179
requirements of 179
tuned coil type 180, 181
BATTERIES
primary 5
secondary 6
Breaker, Circuit
underload 72
Buzzer
excitation systems 167
for adjusting detector 167
tuned tester for direction finder 258
Page
CAPACITY
at radio frequencies, measurement of. .208, 209
distributed, effects of 164
electrostatic 36, 37
equation for 38
formula for standard of 208
measurement of 207, 208
Carborundum Detector
action of 137
adjustment of 139, 140
theory of action 137, 138, 139
tuning circuits for 135
Care of Motor Generator 65
Cargo Transmitting Set, Marconi J/4 K. W.... 248
Cells
primary 5, 6
secondary 6, 7
grouping of 9
in series 9, 10
in parallel 10, 11
in series parallel 11, 12
internal resistance of 10
Charging Panels
Electric Storage Battery Company . 181, 182, 185
General instructions for 187
Marconi auxiliary 180, 182
Choking Coils
high frequency 110, 111
Circuits
branch 13
closed oscillatory 84
divided 13
examples of 13
open oscillatory 84
reaction of coupled 95
receiving radio 129
Closed Circuit Transmitter
calibration of 200
Coils
calculation of inductance of 209, 211, 213
choking 110, 111
measurement of effective inductance of ... 209
measurement natural oscillating period of
tuning 207
induction 46
interrunter for induction 48
Compass, Wireless 255
Condensers
battery of 82
capacity of 37
complete cycle of events in the discharge
of 83
connections for 81
• high potential 81, 110
how to charge 82
low potential 81
motor generators, protective type for 65
short wave If 9
simple 37
Conductors 4
partial 4
Continuous Waves
receivers for 277
transmitters for 2^4
Converter, Rotary 57, 58
Coupling
capacitive °T
coefficient of 9"
conductive 94
direct excitation 93
electrostatic 95
inductive 93, 94
"tight" or "close" .' 96
"tight" and "loose" 219, 2 '0
transmitter, determination of 195
Currents
alternation of 21
by chemical battery 5, 6
by dynamo 22
classification of 4
electric 4
induced 19
of audio frequency, definition of 80
of radio frequency, definition of 80, 81
strength and quantity of 7
thermo-electric 46
319
320
PRACTICAL WIRELESS TELEGRAPHY.
Page
DAMPING OF OSCILLATIONS 90
calculation of 93
measurement of logarithmic decrement
of 200, 201, 202
theory of 83, 90, 91, 92, 93
Decrement
of antenna 126
calculation of 127
Decremeter
calculation of the decrement of 203
Kolster 204
Detectors, Oscillation
carborundum 135
classification of 140, 141
electrolytic 158
holders for 140
magnetic, Marconi 148, 149, 150
primary cell 159
three element valve 159
valve, Fleming 141
zincite-bornite 140
Diagrams, Wiring
Alexanderson alternator 206
arc transmitters 265
auxiliary charging panel 184, 185
beat receiver 281
direction finder 259
earthing system high power stations 305
Glace Bay transmitter 291
Goldschmidt alternator 270
heterodyne receiver 279
Joly-Arco alternator 272
lay out aerials high power stations. .. .298, 299
Marconi duplex scheme 289
Marconi undamped receiver 286
Marconi l/2 K. W. 120 cycle transmitter.. 243
Marconi 2 K. W. 500 cycle transmitter. . 224
Marconi l/2 K. W. 500 cycle trans-
mitter 235, 236
Marconi Y4 K. W. 500 cvcle transmitter.. 251
Marconi 1 K. W. 60 cycle transmitter 241
measurement of decrement 196
Navy "beat" receiver 283
pliotron oscillator 276
radio-frequency amplifier 284
standard receiving tuners. ... 134, 152, 155, 149
standard transmitter 98
tuned coil 181
tuning of transmitters 190, 191, 192, 193
Direction Finder 255
aerials for 256
circuit of 257, 258
direction of forces within 260
general instructions for operation 260, 261
Marconi, description of 255
tuned buzzer tester for 258
to find direction of radio station 262
Dynamo 22
alternating current 26
compound 27, 28
determination of frequency of 24
direct current 27
magnetic field of 24
principle of 22, 23, 24
principle parts of 22
shunt, series and compound 27
simple type of 22, 23
strength of field of 24
Dynamotor 57
EARTH CONNECTION 124, 125
at trans-oceanic stations 125
Edison Storage Battery 79
charge and discharge of 79
Electric Current 14
Electric Meters 42
Electric Motor 29
Electric Waves 87, 88
determination of length of 89
length of 88
standard, for ships aerials 96
wireless 88
velocity of 88
Electrical Circuits 48, 49
examples of 49
Electrical Cells, Grouping of 8
Electrical Devices, Current Output and Voltage
Output of 15
Electrical Horsepower 14
Electrical Resistance 8
Page
Electrical Resonance 85
importance of 188
indicators of 190
Electrical Units 14
practical definition of 14, 15
Electrical Work 13, 14
Electricity
atmospheric 171
frictional 5
static 5
Electrification 5
positive 5
negative 5
Electrodes 6
Electrolyte 6
Electromagnetism 16
Electromotive Force 4
by chemical action 5
by dynamo 22
by friction -. 5
by thermo couple 47
effect of counter 30
induced value of 22
production of 5
unit for 5
Electrostatic Capacity 37
End Turns, receiving tuner 164
switch for 165
FREQUENCY
determination of 24
Dynamo 24
Meter 44
GALVANOMETER •
Construction of 42
Generator
arc, for undamped oscillations 265
compound 28
how to determine polarity of 76
motor 51, 52, 53, 54, 55, 56
series 28
shunt 27
Glace Bay — Clifden Transoceanic Stations.... 291
Goldschmidt Radio-Frequency Alternator. .270, 271
17
. 278
HELIX ,
Heterodyne Receiving System ,
High Power Stations
condensed list of 306
Marconi transoceanic 292
of the United States 305
Horsepower
electrical 14
mechanical 14
Hydrometer 69
INDUCTANCE
calculation of 209, 210, 211, 212, 213
correction factor for calculation of.. ..211, 213
measurement of effective 209
measurement of mutual 216
of an aerial 214, 117, 121
unit of 21
variation of a radio-frequency 165
variometer 166
Induction
electromagnetic 19
magnetic 1
mutual 19
self 20
1 nsulators 4
Bradfield 124
deck 123, 124
fOf.V ARCO STEP-UP FREQUENCY
" TRANSFORMER . 273
KEYS
transmittin
transmitting
Key Control, G. E. Co.'s type,
115
268
MAGNET
permanent
temporary 2
Magnetism
natural
electro 3
INDEX.
321
Page
Magnetic
circuit 3
flux 1
induction 1
permeability 2
polarity 1
poles, laws of 3
retentivity 2
Magnetic Field 3
about two parallel conductors 17
strength of 17, 18
Marconi
balancing out aerials 291
continuous wave receiver 286
continuous wave transmitter 274, 275
directional aerial 292
duplex radio system 290
transoceanic radio telegraphy 288
transoceanic stations 292
tubular mast 299
Measurement
of coupling 195
of decrement 200, 201
of electrostatic capacity 207, 208
of high voltages 220
of inductance of a coil 209
of oscillating period of a coil 207
of receiving transformer 205, 206
of strength of incoming signals 216, 217
of wave length 191, 192, 193
Meters
ammeter 43
audibility meter 217
frequency meter 44
galvanometer 42
hot wire meters ,45, 46
radio frequency meters 47
voltmeter 43
wavemeter 188, 189
wattmeter 43, 44
Motor, Electric 29
counter E. M. F. of 30
field of 30
principle of 29
reversal of 29
torque of 30
with differential field winding 30
Motor Generators 51, 52, 53, 54, 55, 56
care of 65
complete circuit of, with hand starter 63
compound generator type of 53
construction of 51
Crocker- Wheeler type of 54, 55, 56
differential motor type of 54
how to remove armature of 2 K. W. 500
cycle Marconi 66
how to remove armature of % K. W. 500
cycle Marconi 240, 241
regulation of 53
shunt wound 32, 53
Motor Starter 58
automatic % K. W. Marconi type of.. 60, 61
Cutler-Hammer type of 59
General Electric type of 60
2 K. W. automatic 61, 62, 63, 64, 187
2 step y2 K. W. automatic 61
OHMS LAW 11
examples oi 11, 12
Open Circuit Transmitter
calibration of .- 199
Oscillations
damping of 83
determination of frequency of 84
effect of resistance on 84
frequency of 84
generator of 84
highly damped group of 90
logarithmic decrement of Electrical 90
methods of exciting, in an aerial. .. .93, 94, 9!
of feeble damping 90
variation of frequency of 85
Oscillation Constant 86
Oscillation Transformer
adjustment of coupling of 107
inductive type 107, 108
pancake type 108
square coil type iuv
variometer type 108
Oscillator
open circuit 86
Pliotron 276
Page
PANEL TRANSMITTERS, AMERICAN
MARCONI TYPE 223
general instructions for 253
Phase Displacement of alternating currents. . . 41
Polarity
Magnetic 1
Power Circuits
examples of 48, 49
Power Factor 41
Protective Condensers for Motor Generator. . . 64
Protective Resistance Rods for Motor Generator 64
RADIATION OF ELECTRIC WAVES... 87, 125
Radio-frequency current, generation of 80, 81
Radiogoniometer 255, 257
Radio Measurements, Practical 189
Radio Transmitter 79
appliances for 101, 115
explanation of 99, 100
fundamental circuit of 97
numerical values for 100
spark dischargers for
101, 102, 103, 104, 105, 106
Marconi panel types 223
Range
calculation of transmission 127
Reactance
capacity 38
inductance 39
regulators 114
Receiver
balanced crystal 172
capacitively coupled 134
directly coupled 133, 134
electrostatically coupled 134
impedance of telephone 131
inductively coupled 132, 133
simple radio 132
telephone magneto 131
Receiving Sets
long distance 306
Marconi balanced crystal 172
Marconi-Fleming valve 141
Marconi multiple tuner 148
Marconi type 101 154
Marconi type 106 151
Marconi type 107-a 144
Marconi Universal 157
Rectifier 131
Relays
Brown 170
microphonic 169
Resistance, Electrical 8
examples of 9
radiation 126
relative, of metals 9
specific 8
standard of 9
unit of 9
Resonance Curves, Plotting of... 196, 197, 198, 199
Resonance, Electrical 40, 85
indicators of, for wavemeters. 191
resonance in complete radio systems 135
Rheostat Field 26
construction of 57
Rotary Converter 51
SELF INDUCTION
coefficient of 21
unit of 21
Signals. Radio
audibility meter for strength of 217
chart showing variation of : . 218
measurement of strength of incoming. .216, 217
Solenoid 17
Spark Discharge
analysis of 83
Spark Dischargers
adjustment of note of 106
adjustment of quenched 247
details of quenched 230
Non-synchronous 102, 103
plain -. 101
quenched 105
synchronous 103, 104
synchronous, 240 cycle 248
Static Electricity 5, 171
Starters. Motor. .. 58
322
PRACTICAL WIRELESS TELEGRAPHY.
Page
Storage Batteries 67
ammeter and underload circuit breaker for
charging circuit of '. . . . 72
acid spray of 77
capacity of . 69
charging process ot oo
charging when voltage of charging source
is less than that of . 74
determination of state of charge and dis-
charge of 76
Edison type of 79
electrolyte of 69
Exide type of, general instructions
fundamental actions of 68, 69
fundamental facts of .
general construction and action of 68
how to determine charging resistance 71
lamp bank resistance for 72
lead sulphating of • • • 69
level of electrolyte of 77
necessity for 67
overcharge of 74
portable chloride type of, general instruc-
tions 77
specific gravity of • • 69
use of ampere hour meter for 72, 73
Switch
aerial change-over 1 14
end turn • • • 165
type I, aerial, Marconi 173, 174
TELEPHONES
Baldwin 168,
receiving
response of
Tikker Detector
Tone Wheel Detector
Transformers, A. C
closed core
high voltage
magnetic circuit of
magnetic leakage gap for
open core " 35,
oscillation
radio-frequency
receiving radio ii
step-down 34
step-up
Transmitters
aerial current of
auxiliary
Marconi panel type of ....... .... .... . . . . .
Marconi type Jr-4 ZZb, z/o, zz/, zzo,
Marconi type P-5
234, 235, 236, 237, 238, 239,
radio
reduction of power of
type E-2, details and circuits of 244,
type E-2, instructions for tuning of
type E-2, Marconi
type P-4, tuning of 231, 232, 233,
type P-4, adjustment of 229, 230,
type P-5, description of
234, 235, 236, 237, 238,
type P-5, Marconi adjustment of 239,
type P-9, description
type P-9, Marconi ^4 K. W
type P-9, tuning of
] K. W. 60 cycle non-synchronous
1 K. W. 60 cycle, description of
1 K. W. adjustment of
1 K. W. installation of
-Tuned Coil Emergency Transmitter 180,
Tuners, Receiving
balanced crystal .............
calibration open and closed circuits sim-
ultaneously J • ' '• one
calibration of secondary and primary . .*JUo,
end turns of :
English Marconi Universal.. • •••
general advice for manipulation of.... 1/6,
inductively coupled, adjustment of
169
167
131
278
284
33
112
35
113
112
107
36
49
34
179
229
80
253
245
246
244
234
231
239
240
249
248
252
240
241
242
242
181
J29
207
Page
Tuners, Receiving — Continued.
Marconi multiple '. 148, 149, 150
Marconi type 101 154, 155, 156
Marconi type 106 151, 152, 153, 154
Marconi type 107-a 144, 145, 146, 147
selectivity in 136, 137
theory of adjustment of 136, 137
Marconi type 112 174, 175, 176
Tuning 188
aerial inductance for 109, 110
by hot wire ammeter 194
continuously variable inductance for 109
general instructions for radio transmitter. 191
measurement of the closed circuit 193
measurement of the open circuit 192
measurement of radiated wave 193, 194
of the 2 K. W. 500 cycle panel trans-
mitter 194, 195
Tuning Records
Marconi 220
U. S. Government 221
UNDAMPED OSCILLATIONS
Alexanderson alternator >for 268
arc generator of 265
beat receiver for 280, 281
Goldschmidt alternator for 270, 271
heterodyne system for 278, 279
Joly-Arco system for 273, 274
Marconi's system for 274, 275
Marconi's receivers for 286
methods of generating 264, 265
Navy beat receiver for 283
receivers for 277
tikker receiver for 278
tone wheel for 284
transmitters of 264
Units, Electrical 14, 15
of current 7, 8
of electromotive force 7, 14
of power 14, 15
prefixes of 15
of quantity 8, 1'
of resistance 9, 14
VALVE, OSCILLATION
adjustment of 161
amplifier circuits for 163
as combined detector, amplifier and beat
receiver •.•••.• -280, 281
as source of radio-frequency oscillations. . 280
audio- frequency repeater for 161
circuits for Fleming 143
Fleming 141, 142
operation of 3 element valve 160
radio-frequency amplifier 163
regeneiative circuits for 162
repeater circuit for 161
three element 159
U. S. Navy circuits for 283
Variometer
for receiver 166
for transmitter 108
Voltmeter 42
WATTMETER 43, 44
Wavemeter
as a source of high-frequency oscillations. 205
calibration of 214, 215
measurement of natural wave length by 190, 191
resonant adjustment of 190, 191
uses of 190
Waves
damped 8}
distortion ot 1^4
method of changing length of 97
Naval standard length of • • • 97
standard commercial wireless o<
sustained, apparatus for.... 265, 266, 267, 268
undamped °
363013
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